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Method: Comparison of surveys used to measure physical activity

Method: Comparison of surveys used to measure physical activity Abstract Objective: To compare the level of agreement in results obtained from four physical activity (PA) measurement instruments that are in use in Australia and around the world. Methods: 1,280 randomly selected participants answered two sets of PA questions by telephone. 428 answered the Active Australia (AA) and National Health Surveys, 427 answered the AA and CDC Behavioural Risk Factor Surveillance System surveys (BRFSS), and 425 answered the AA survey and the short International Physical Activity Questionnaire (IPAQ). Results: Among the three pairs of survey items, the difference in mean total PA time was lowest when the AA and NHS items were asked (difference=24) (SE:17) minutes, compared with 144 (SE:21) mins for AA/BRFSS and 406 (SE:27) mins for AA/IPAQ). Correspondingly, prevalence estimates for ‘sufficiently active’ were similar for AA and NHS (56% and 55% respectively), but about 10% higher when BRFSS data were used, and about 26% higher when the IPAQ items were used, compared with estimates from the AA survey. Conclusions: The findings clearly demonstrate that there are large differences in reported PA times and hence in prevalence estimates of ‘sufficient activity’ from these four measures. Implications: It is important to consistently use the same survey for population monitoring purposes. As the AA survey has now been used three times in national surveys, its continued use for population surveys is recommended so that trend data over a longer period of time can be established. (Aust N Z J Public Health 2004; 28: 128-34) Wendy Brown School of Human Movement Studies, University of Queensland Adrian Bauman, Tien Chey School of Public Health and Community Medicine, University of New South Wales Stewart Trost School of Human Movement Studies, University of Queensland Kerry Mummery School of Health and Human Movement Studies, Central Queensland University, Queensland n Australia, survey instruments for the assessment of physical activity (PA) have evolved over time, from those used in the early cardiovascular disease risk factor surveys1 to those now used for population monitoring. As is the case in other countries, several different instruments are used to assess population levels of activity in Australia. For example, at the national level, the Australian Bureau of Statistics (ABS) included nine items to assess PA in its fiveyearly National Health Surveys (NHS) in 1989, 1995 and 2001,1 while a different PAspecif ic survey was developed to evaluate the Active Australia campaign in 1997, 1999 and 2000. 2 Both these surveys offer the opportunity to assess trends in PA over time. However, in some States, there has been interest in using the PA items that form part of the US CDC Behavioural Risk Factor Surveillance System (BRFSS),3 and in the International Physical Activity Questionnaire (IPAQ), a newer survey developed by a group of international researchers (including several Australians) that has undergone reliability and validity testing in 12 countries.4 Each instrument includes consideration of frequency and duration of a range of activities of def ined intensity, such as walking, ‘moderate’ or ‘vigorous’ activity. Frequency is usually assessed as the number of days or number of sessions of activity in a defined period, such as ‘last week,’ ‘last seven days,’ ‘a usual week’ or ‘the last two weeks’, etc. Duration is usually reported for either the same time period (e.g. last week, last two weeks) or for a typical day when the activity was undertaken in that time period. It is generally reported in hours and minutes and is usually summed across the domains of walking, moderate and vigorous-intensity activity, to provide an indication of total physical activity time over the reporting period. Some measures also ask about selfrated intensity of participation in the nominated activities. The primary measurement goal in all these surveys is to provide an estimate of whether respondents reach an energy expenditure threshold which is sufficient to be of health benefit. In Australia, this is usually defined as participation for a specified minimum time (150 minutes) in activities of at least ‘moderate’ intensity (i.e. with energy expenditure at least three times the resting rate, or ≥3 ‘metabolic equivalents’ or ‘METs’5) accumulated over at least f ive days each week. Submitted: June 2003 Revision requested: September 2003 Accepted: October 2003 Correspondence to: Professor Wendy Brown, School of Human Movement Studies, University of Queensland, St Lucia, Queensland 4072. Fax: (07) 3365 6877; e-mail: wbrown@hms.uq.edu.au AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2004 VOL. 28 NO. 2 Methods Comparison of PA surveys Very little is known about the comparability of different surveys in terms of estimating the proportion of the population that is sufficiently active for health benef it. The main aim of this study was therefore to compare the level of agreement in prevalence estimates derived from four instruments that are in use in Australia and elsewhere around the world. Data management and scoring protocols Four different measures were used to compare the results of each survey, based on different interpretations of the evidence on the health benefits of physical activity. Total time in physical activity: Total minutes of walking, moderate and/or vigorous-intensity physical activity were summed, with time spent in vigorous activity weighted by a factor of two, to account for its greater intensity.2 150 minutes: Based on the National PA Guidelines,6 “sufficient activity for health” was first defined as “accumulation of 150 minutes or more of at least moderate intensity physical activity in a week (with time in vigorous activity weighted by two)”. 150 minutes and five sessions: A second def inition of ‘sufficient activity’ was developed to take account of the current guidelines, which advise that 30 minutes of moderate intensity physical activity on most days of the week is sufficient to confer health benef its.2,7 For this definition, the criterion for ‘sufficient activity’ was defined as 150 minutes of walking, moderate and vigorous activity (with time in vigorous activity weighted by a factor of two) accrued in at least five sessions or five days of activity in a week. Sedentariness: The final measure was based on the proportion of people who were “sedentary or physically inactive”, defined as no participation (i.e. no sessions ≥10 minutes) in any walking, moderate or vigorous physical activity. Coding and truncation rules were developed to derive each of these four measures from each survey, taking into account Methods Recruitment and data collection The sample was drawn at random from the regularly updated electronic database of telephone numbers in Rockhampton, Queensland, with replacement of duplicate, mobile and business numbers, as well as of numbers for nursing homes and other collective dwellings. Calls were made using a CATI system in August and September 2001, as part of the baseline data collection for a physical activity intervention study. Each interviewer asked consenting participants to answer the Active Australia survey and one of the other three surveys: either the BRFSS, the short form of the IPAQ or the NHS physical activity questions. The order of administration of the two surveys was randomly generated by the Ci3 CATI system (Sawtooth Software, Evanston, Illinois), with a random half of each group answering the AA questions first, and the remainder answering the other questions f irst. The study protocol was approved by the Human Ethics Research Review Panel at Central Queensland University. Table 1: Coding and truncation rules for derivation of the four measures from each survey. Active Australia National Health Survey Behavioural Risk Factor Surveillance System ∑ (# days x usual time in each activity in the last 7 days) M + (Vx2) ≥150 minutes/week or W + M + (Vx2) ≥150 minutes/week M+(Vx2) ≥150 minutes/week AND ≥5 sessions or W + M + (Vx2) ≥150 minutes/week AND ≥5 sessions International Physical Activity Questionnaire – short version ∑ (# days x time per day in each activity in a usual week) W(all) + M + (Vx2) ≥150 minutes/week or W(mv) + M + (Vx2) ≥150 minutes/week W(all) +M+(Vx2) ≥150 minutes/week AND ≥5 sessions or W(mv) + M + (Vx2) ≥150 minutes/week AND ≥5 sessions Measure 1 Total time calculation for each activity Measure 2 150 minutes ∑ (# of times x time spent in each activity in the last week) ∑ (# of times x total time in each activity in last two weeks/2) W(t) + W(r) + M + (Vx2) W + M + (Vx2) ≥150 minutes/week ≥150 minutes/week or W(t) + W(r) + M + (Vx2) + VG ≥150 minutes/week W(t) + W(r) + M + (Vx2) ≥ 150 minutes/week AND ≥ 5 sessions or W(t) + W(r) + M + (Vx2)+VG ≥150 minutes/week AND ≥5 sessions W + M + (Vx2) ≥150 minutes/week AND ≥5 sessions Measure 3 150 mins and 5 sessions Measure 4 Inactivity Truncation rules Proportion reporting NO activity (≥10 minutes at a time) For each activity (walking, moderate, vigorous activity) weekly minutes truncated to a maximum of 840 minutes (2 hours per day or 14 hours per week). The sum of total weekly time in all activities truncated 1,680 minutes (4 hours per day or 28 hours per week). Notes: W = time spent walking; [W(t) = walking to/from places (AA); W(r) = walking for recreation or leisure (AA); W(all) = all walking (BRFSS and IPAQ); W(mv) = moderate and vigorous paced walking (IPAQ)]. M = time spent in moderate intensity activities. V = time spent in vigorous activities. 2004 VOL. 28 NO. 2 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Brown et al. Article differences in the individual items asked in each survey (see Table 1). For example, in the NHS, the number of minutes and sessions reported in the last two weeks was divided by two to give weekly times/sessions. In some cases, more than one interpretation of each measure was derived. For example, in the AA survey, one interpretation of the first three measures did not include time spent in “gardening or heavy yardwork” [four item AA (AA4)], while a second interpretation did [five item AA (AA5)]. Similarly, for the BRFSS, one interpretation included time spent in an additional walking question [three item BRFSS (BRFSS3)], while the second only included walking as part of the moderate intensity question [two item BRFSS (BRFSS2)]. For IPAQ, the first three measures were calculated (a) including all paces of walking (IPAQ) and (b) including only walking reported to be at moderate or vigorous pace (IPAQmv). These variations are summarised in Table 1. Note that for the AA survey, the walking question was split into two (walking ‘to and from places’ and ‘for recreation or pleasure’) and the responses were summed. Table 2: Numbers of participants in each age and sex group who completed each pair of surveys. Active Australia and NHS 18-44 years Men Women 45-59 years Men Women 60-75 years Men Women Total 112 119 42 45 47 63 428 Active Australia and BRFSS Active Australia and IPAC ducted using SAS version 8.02 (SAS Institute Inc., Cary NC, USA 1999-2001). Statistical analyses Means and quartiles were calculated for total time in activity derived from each survey and for the total number of days/ sessions of reported activity. Differences between the three pairs of measures were computed and displayed graphically using mean and difference plots.8 For the three categorical measures, ‘per cent agreement’ was calculated for both measures of ‘sufficiently active’ (150 minutes, and 150 minutes and five sessions) and for ‘sedentariness’. The consistency with which participants were classified as ‘sufficiently active’ or ‘insufficiently active’ and as ‘sedentary’ or ‘not-sedentary’ on each survey, correcting for chance agreement, was also assessed using Cohen’s Kappa.9 All analyses were con- Results Participants The overall response rate was 51%. Of the 1,280 participants, 428 answered the Active Australia and NHS surveys, 427 answered the AA and BRFSS and 425 answered the AA and IPAQ surveys. There was a similar distribution of men and women in each of three age groups in each survey group (see Table 2). Their education levels were similar to those reported for a random Queensland sample in 2001, with 39% having fewer than 12 years of education (37% in the Queensland sample), 18% having completed year 12 (19%), 24% with a trade or similar qualification (26%) and 19% with a diploma or degree (18%).10 The Table 3: Means and quartiles for total time and frequency of activity derived from each survey. Comparisons of measures AA4 AA5 NHS AA4 AA5 BRFSS2 BRFSS3 AA4 AA5 IPAQ IPAQmv Total time (weekly reported minutes) and distributional quartiles (minutes) Mean (SE) 25% 50% 75% 327 (18.4) 406 (19.8) 303 (17.4) 317 (16.8) 399 (19.9) 461 (21.1) 761 (27.4) 353 (18.9) 450 (20.8) 918 (27.9) 856 (28.1) 60 100 36 40 90 90 240 53 95 430 360 180 270 180 210 253 310 720 210 300 870 840 480 600 428 480 590 840 1180 585 720 1500 1380 Frequency (days/sessionsa) and quartiles (days) Mean (SE) 25% 50% 75% 5.9 (6.5) 6.6 (6.6) 4.6 (4.9) 5.5 6.4 5.0 8.9 5.3 6.4 8.8 8.2 (5.2) (5.6) (4.5) (6.1) (4.9) (5.2) (5.8) (5.9) 1 2 1 2 2 2 5 2 2 4 3 4 5 3 5 5 5 9 4 5 8 7 8 9 6.5 7 9 7 12 8 9 13 12 Notes: (a) Note that more than 7 sessions/days can be accrued per week, by summing across walking, moderate and vigorous questions. AA4 = four item Active Australia (both walking questions, moderate and vigorous activities, not including gardening). AA5 = five item Active Australia (both walking questions, moderate and vigorous activities and gardening). NHS= National Health Survey, walking, moderate and vigorous. BRFSS2 = two item BRFSS, moderate and vigorous activities only. BRFSS3= three item BRFSS, including walking, moderate and vigorous activities. IPAQ = all paces of walking, plus moderate and vigorous activities. IPAQmv = only moderate and vigorous paced walking, and other moderate and vigorous activities. SE = standard error. AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2004 VOL. 28 NO. 2 Methods Comparison of PA surveys respondents were similar to the Australian population in terms of the proportion categorised as ‘adequately active for health benefit’ on the AA survey (43.2% of this sample and 45.2% nationally). Prevalence data – ‘sufficient physical activity’ Measures of agreement for the prevalence of ‘sufficiently active’ and ‘sedentariness’ from the three pairs of surveys are shown in Table 4. This table shows the proportions meeting the 150minute criterion (top panel), the proportions meeting both the 150 minutes and f ive days/sessions criteria (middle panel), and the proportions reporting no activity (bottom panel). Per cent agreement coefficients and kappa coefficients with 95% confidence intervals are shown for the paired data in each row. The f irst row of data shows that prevalence estimates from AA and NHS were similar, especially when AA4 data were used. Compared with AA 4, prevalence was about 10% higher when BRFSS data were used. However, there was closer agreement between prevalence estimates from BRFSS and AA5, but the Kappa scores were in the modest range. When walking was ‘double counted’ in the five item BRFSS, prevalence estimates were much higher but the per cent agreement and Kappa scores were not markedly changed. The relationship between the AA and the short IPAQ questionnaire indicates that use of the IPAQ survey resulted in much higher prevalence estimates than the AA instrument, across all modes of measurement. For example, there was a prevalence difference of around 26% between the AA 4 and the short IPAQ on the criterion of 150 minutes per week. When the 150 minutes and f ive sessions criteria were used, the relationships between the three pairs of surveys were similar to those described above, but the prevalence estimates were between 13% and 19% lower than when the single 150 minutes criterion was used (see Table 4, middle panel). Total time and number of days/sessions Means and quartiles for total activity time and for frequency of days/sessions reported for each pair of surveys are shown in Table 3. The difference in mean total activity time between the NHS and the four item AA survey (AA4, without vigorous yard work or gardening) was 24 minutes (SE:17). When the AA survey was compared with the BRFSS, the differences were much larger (see middle panel of Table 3). The BRFSS total from the moderate and vigorous questions, without the additional ‘double counted’ walking question, was 144 (SE:21) minutes more than the AA 4 total. However, when the time spent in gardening item was added to the AA total (AA5) the mean difference was only 62 (SE:21) minutes. The addition of the BRFSS ‘walking question’ increased the total time estimate by 362 or 444 minutes when compared with AA5 or AA 4 respectively. The differences in mean total time from the AA and short IPAQ surveys are shown in the bottom panel of Table 3. When only vigorous and moderately paced walking time was included in the IPAQ total, the difference (compared with AA5) was 468 (SE:27) minutes, and when all walking was included in the IPAQ total the difference was 406 (SE:27) minutes. Differences between these two surveys amounted to more than 500 minutes per week when AA 4 results were used. These differences between the times reported in the AA4 and the other three surveys are illustrated graphically using Bland and Altman plots in Figure 1. From these, it is clear that there was reasonable agreement between the AA 4 and NHS surveys (mean difference close to zero), but the funnel shape that is evident in all three graphs indicates that absolute agreement worsened as the average time reported increased. Given that most of the health benef its of PA are seen with PA durations of up to one hour per day (about 400 minutes per week), it is of less concern in terms of PA measurement that the poorest agreement was seen for levels of about 800 minutes per week. The same pattern was evident for the other two comparisons, but with a much larger mean difference for the IPAQmv and AA4 comparison. The data in Table 3 also show the mean number of times (AA, NHS) or days (IPAQ, BRFSS) reported in each pair of surveys. The patterns of difference between the surveys were similar to those described for total minutes (above), with the lowest frequency reported for the NHS, and highest for the BRFSS and IPAQ. Analysis of the order of survey administration found very little ordering effect of the questions in the comparisons between AA and both NHS and BRFSS. However, in the AA and IPAQ comparison, there was a trend for AA to score more total minutes and number of days/sessions when IPAQ was asked first, compared with the results when AA was asked first, but the trend was not statistically significant (data not shown). 2004 VOL. 28 NO. 2 Prevalence data – sedentariness The data in the lower panel of Table 4 show that, in general, the more items included in each version of each survey, the lower the prevalence of sedentariness, with overall estimates of sedentariness higher when the AA, NHS and two item BRFSS were used. Per cent agreement scores were higher than those shown for ‘activity’ but Kappa scores were lower for sedentariness than for ‘activity’ in the AA/NHF and AA/BRFSS comparisons. Discussion The aim of this study was to compare agreement between prevalence estimates for ‘sufficient activity’ derived from four survey instruments, using a randomly selected population sample. The AA survey was used as a ‘reference’ as it is in current population use for PA surveillance in Australia. The comparison instruments were the ‘traditional’ Australian NHS measure, the US BRFSS, and the recently developed IPAQ. The f indings clearly demonstrated that there were large differences in the reported PA times and hence in the prevalence estimates of ‘sufficient activity’ from these four measures. The highest level of agreement was between the AA and NHS and the poorest was between the AA and IPAQ. This reflects the different ‘domains’ of activity included in each survey. Traditionally, PA surveys have focused on leisure-time PA (LTPA), because, until the mid 1990s, the health benefits of PA were largely attributed to AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Brown et al. Article Figure 1a-c: Plots of differences in total weekly minutes for pairs of comparison surveys (y axis), against the average time reported in the two surveys (x axis). 1a: comparison of NHS v AA4; 1b: comparison of BRFSS2 v AA4; 1c: comparison of IPAQmv v AA4. Figure 1a Weekly minutes (NHS, AA4) Difference in minutes (NHS-AA4) Average in minutes (NHS and AA4) Figure 1b Weekly minutes (BRFSS2, AA4) Difference in minutes (BRFSS2 -AA4 ) Average in minutes (BRFSS2 and AA4) Figure 1c Weekly minutes (IPAQmv, AA 4) Difference in minutes (IPAQmv-AA4) Average in minutes (IPAQmv and AA4) AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2004 VOL. 28 NO. 2 Methods Comparison of PA surveys participation in more vigorous forms of activity such as organised sport and fitness. More recently, as interest in the obesity epidemic has focused our attention on total energy expenditure, there have been attempts to include different domains of activity, such as transport and occupational activity, in PA surveys.1 In some cultures, energy expended in work and transport contributes much more to total energy expenditure than LTPA, and the IPAQ survey probably does best at ‘capturing’ activity in all these domains. As a result, the minutes of PA reported in response to the IPAQ survey are higher than for the other three surveys, and prevalence estimates are concomitantly higher. This has implications for policy, as prevalence estimates are used to derive the population attributable risks of behaviours, which are in turn used to determine priority areas for public health action. For example, using the NHS, AA 4, and BRFSS2 we would estimate that about half the population is not sufficiently active for health benef it, compared with 20-30% using IPAQ. More research into the relative health benefits of activity in each PA domain is required to assess whether the ‘threshold’ for categorising ‘activity’ should be changed if more domains are included, and criterion-based validity data are urgently required for all four of these surveys. One contributing factor to the higher times reported in the IPAQ may be that this survey was the only one of the four to ask respondents to think about a ‘usual’ week. While this will overcome any problems relating to the fact that the ‘last week’ may be Table 4: Per cent agreement and Kappa scores for the proportion of participants categorised as ‘sufficiently active’ (a) using the criterion of 150 minutes/week (top panel), (b) using the criterion of 150 minutes and 5 sessions/week (middle panel), and (c) for the proportion of participants categorised as ‘sedentary’ (no physical activity of any kind reported, bottom panel) for each pair of surveys. Active Australia (a) 150 min/week AA4 Alternative NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv AA prevalence Alternative prevalence % agreement Kappa (95% CI) 0.50 0.34 0.26 0.31 0.32 0.44 0.35 0.29 0.40 0.41 0.47 0.36 0.24 0.35 0.37 0.40 0.38 0.26 0.45 0.46 0.41 0.26 0.25 0.31 0.37 0.30 0.21 0.26 0.36 0.45 (0.42-0.58) (0.25-0.43) (0.18-0.34) (0.23-0.39) (0.24-0.40) (0.35-0.52) (0.26-0.45) (0.20-0.38) (0.30-0.49) (0.31-0.50) (0.38-0.55) (0.27-0.45) (0.17-0.31) (0.28-0.42) (0.29-0.44) (0.31-0.48) (0.29-0.47) (0.18-0.35) (0.37-0.53) (0.37-0.54) (0.29-0.52) (0.14-0.37) (0.13-0.37) (0.18-0.43) (0.24-0.50) (0.19-0.42) (0.09-0.33) (0.11-0.40) (0.20-0.52) (0.30-0.60) AA5 (b) 150 min/week PLUS 5 sessions AA4 AA5 (c) Sedentary AA4 AA5 Notes: AA4 = four item Active Australia (both walking questions, moderate and vigorous activities, not including gardening). AA5 = five item Active Australia (both walking questions, moderate and vigorous activities and gardening). NHS= National Health Survey, walking, moderate and vigorous activities. BRFSS2 = two item BRFSS, moderate and vigorous activities only. BRFSS3= three item BRFSS, including walking, moderate and vigorous activities. IPAQ = all paces of walking, plus moderate and vigorous activities. IPAQmv = only moderate and vigorous paced walking, and other moderate and vigorous activities. CI = confidence interval 2004 VOL. 28 NO. 2 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Brown et al. Article atypical due to illness or holidays, it is likely that this form of questioning will result in more socially acceptable, and therefore more inflated responses. It may also be true that between survey differences are attributable in part to the assessment of activity duration. Notably, the BRFSS and the IPAQ require respondents to estimate the amount of time spent in each activity domain on a single day. In contrast, the AA and NHS ask respondents to estimate the time spent in each activity domain for the entire recall period. Given that physical activity behaviour exhibits considerable day-to-day variability,4,11 it is possible that estimating the ‘usual’ or ‘average’ duration of activity on a single day may be inherently more difficult for respondents than recalling the duration of each activity session performed and summing over the entire recall period. One of the strengths of this study was that we used a randomly selected population sample with PA patterns similar to those previously reported in Australia.2 A limitation of the study was that participants were asked to respond to two surveys on one occasion, and their responses to one survey may have influenced their responses to the other. However, the order of administration of the surveys did not greatly affect the results. Overall, this study has demonstrated the difficulty of intersurvey comparison when surveys are designed to include different domains of physical activity. Each survey ‘captures’ different dimensions of total physical activity, ranging from the relatively narrow leisure time PA focus of the NHS to the more inclusive IPAQ survey, which attempts to have respondents think about all types of daily activity at work, at home and during recreation. Given that the variability between methods does not show consistent patterns, it is not possible to develop algorithms to translate prevalence estimates obtained from different surveys. In light of this, and of the public health need to track trends in PA over time, it is important to consistently use the same survey for population monitoring purposes. In Australia, the NHS items have been used by the ABS since 1985, but prevalence estimates are lower than for the other three surveys because of the focus on more ‘structured’ leisure-time activities. The AA survey was developed with a view to capturing more of the ‘moderate intensity’ activity associated with today’s lifestyle. As it has now been used three times in national surveys and as it appears to perform as well as any of the available alternatives, its continued use for population surveys is recommended so that trend data over a longer period of time can be established. The IPAQ survey may be useful for evaluation of intervention trials, when more details about changes in different domains of physical activity are required. Acknowledgements This work was supported by a grant from the Australian Commonwealth Department of Health and Ageing. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Australian and New Zealand Journal of Public Health Wiley

Method: Comparison of surveys used to measure physical activity

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Publisher
Wiley
Copyright
2004 The Public Health Association of Australia Inc
ISSN
1326-0200
eISSN
1753-6405
DOI
10.1111/j.1467-842X.2004.tb00925.x
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Abstract

Abstract Objective: To compare the level of agreement in results obtained from four physical activity (PA) measurement instruments that are in use in Australia and around the world. Methods: 1,280 randomly selected participants answered two sets of PA questions by telephone. 428 answered the Active Australia (AA) and National Health Surveys, 427 answered the AA and CDC Behavioural Risk Factor Surveillance System surveys (BRFSS), and 425 answered the AA survey and the short International Physical Activity Questionnaire (IPAQ). Results: Among the three pairs of survey items, the difference in mean total PA time was lowest when the AA and NHS items were asked (difference=24) (SE:17) minutes, compared with 144 (SE:21) mins for AA/BRFSS and 406 (SE:27) mins for AA/IPAQ). Correspondingly, prevalence estimates for ‘sufficiently active’ were similar for AA and NHS (56% and 55% respectively), but about 10% higher when BRFSS data were used, and about 26% higher when the IPAQ items were used, compared with estimates from the AA survey. Conclusions: The findings clearly demonstrate that there are large differences in reported PA times and hence in prevalence estimates of ‘sufficient activity’ from these four measures. Implications: It is important to consistently use the same survey for population monitoring purposes. As the AA survey has now been used three times in national surveys, its continued use for population surveys is recommended so that trend data over a longer period of time can be established. (Aust N Z J Public Health 2004; 28: 128-34) Wendy Brown School of Human Movement Studies, University of Queensland Adrian Bauman, Tien Chey School of Public Health and Community Medicine, University of New South Wales Stewart Trost School of Human Movement Studies, University of Queensland Kerry Mummery School of Health and Human Movement Studies, Central Queensland University, Queensland n Australia, survey instruments for the assessment of physical activity (PA) have evolved over time, from those used in the early cardiovascular disease risk factor surveys1 to those now used for population monitoring. As is the case in other countries, several different instruments are used to assess population levels of activity in Australia. For example, at the national level, the Australian Bureau of Statistics (ABS) included nine items to assess PA in its fiveyearly National Health Surveys (NHS) in 1989, 1995 and 2001,1 while a different PAspecif ic survey was developed to evaluate the Active Australia campaign in 1997, 1999 and 2000. 2 Both these surveys offer the opportunity to assess trends in PA over time. However, in some States, there has been interest in using the PA items that form part of the US CDC Behavioural Risk Factor Surveillance System (BRFSS),3 and in the International Physical Activity Questionnaire (IPAQ), a newer survey developed by a group of international researchers (including several Australians) that has undergone reliability and validity testing in 12 countries.4 Each instrument includes consideration of frequency and duration of a range of activities of def ined intensity, such as walking, ‘moderate’ or ‘vigorous’ activity. Frequency is usually assessed as the number of days or number of sessions of activity in a defined period, such as ‘last week,’ ‘last seven days,’ ‘a usual week’ or ‘the last two weeks’, etc. Duration is usually reported for either the same time period (e.g. last week, last two weeks) or for a typical day when the activity was undertaken in that time period. It is generally reported in hours and minutes and is usually summed across the domains of walking, moderate and vigorous-intensity activity, to provide an indication of total physical activity time over the reporting period. Some measures also ask about selfrated intensity of participation in the nominated activities. The primary measurement goal in all these surveys is to provide an estimate of whether respondents reach an energy expenditure threshold which is sufficient to be of health benefit. In Australia, this is usually defined as participation for a specified minimum time (150 minutes) in activities of at least ‘moderate’ intensity (i.e. with energy expenditure at least three times the resting rate, or ≥3 ‘metabolic equivalents’ or ‘METs’5) accumulated over at least f ive days each week. Submitted: June 2003 Revision requested: September 2003 Accepted: October 2003 Correspondence to: Professor Wendy Brown, School of Human Movement Studies, University of Queensland, St Lucia, Queensland 4072. Fax: (07) 3365 6877; e-mail: wbrown@hms.uq.edu.au AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2004 VOL. 28 NO. 2 Methods Comparison of PA surveys Very little is known about the comparability of different surveys in terms of estimating the proportion of the population that is sufficiently active for health benef it. The main aim of this study was therefore to compare the level of agreement in prevalence estimates derived from four instruments that are in use in Australia and elsewhere around the world. Data management and scoring protocols Four different measures were used to compare the results of each survey, based on different interpretations of the evidence on the health benefits of physical activity. Total time in physical activity: Total minutes of walking, moderate and/or vigorous-intensity physical activity were summed, with time spent in vigorous activity weighted by a factor of two, to account for its greater intensity.2 150 minutes: Based on the National PA Guidelines,6 “sufficient activity for health” was first defined as “accumulation of 150 minutes or more of at least moderate intensity physical activity in a week (with time in vigorous activity weighted by two)”. 150 minutes and five sessions: A second def inition of ‘sufficient activity’ was developed to take account of the current guidelines, which advise that 30 minutes of moderate intensity physical activity on most days of the week is sufficient to confer health benef its.2,7 For this definition, the criterion for ‘sufficient activity’ was defined as 150 minutes of walking, moderate and vigorous activity (with time in vigorous activity weighted by a factor of two) accrued in at least five sessions or five days of activity in a week. Sedentariness: The final measure was based on the proportion of people who were “sedentary or physically inactive”, defined as no participation (i.e. no sessions ≥10 minutes) in any walking, moderate or vigorous physical activity. Coding and truncation rules were developed to derive each of these four measures from each survey, taking into account Methods Recruitment and data collection The sample was drawn at random from the regularly updated electronic database of telephone numbers in Rockhampton, Queensland, with replacement of duplicate, mobile and business numbers, as well as of numbers for nursing homes and other collective dwellings. Calls were made using a CATI system in August and September 2001, as part of the baseline data collection for a physical activity intervention study. Each interviewer asked consenting participants to answer the Active Australia survey and one of the other three surveys: either the BRFSS, the short form of the IPAQ or the NHS physical activity questions. The order of administration of the two surveys was randomly generated by the Ci3 CATI system (Sawtooth Software, Evanston, Illinois), with a random half of each group answering the AA questions first, and the remainder answering the other questions f irst. The study protocol was approved by the Human Ethics Research Review Panel at Central Queensland University. Table 1: Coding and truncation rules for derivation of the four measures from each survey. Active Australia National Health Survey Behavioural Risk Factor Surveillance System ∑ (# days x usual time in each activity in the last 7 days) M + (Vx2) ≥150 minutes/week or W + M + (Vx2) ≥150 minutes/week M+(Vx2) ≥150 minutes/week AND ≥5 sessions or W + M + (Vx2) ≥150 minutes/week AND ≥5 sessions International Physical Activity Questionnaire – short version ∑ (# days x time per day in each activity in a usual week) W(all) + M + (Vx2) ≥150 minutes/week or W(mv) + M + (Vx2) ≥150 minutes/week W(all) +M+(Vx2) ≥150 minutes/week AND ≥5 sessions or W(mv) + M + (Vx2) ≥150 minutes/week AND ≥5 sessions Measure 1 Total time calculation for each activity Measure 2 150 minutes ∑ (# of times x time spent in each activity in the last week) ∑ (# of times x total time in each activity in last two weeks/2) W(t) + W(r) + M + (Vx2) W + M + (Vx2) ≥150 minutes/week ≥150 minutes/week or W(t) + W(r) + M + (Vx2) + VG ≥150 minutes/week W(t) + W(r) + M + (Vx2) ≥ 150 minutes/week AND ≥ 5 sessions or W(t) + W(r) + M + (Vx2)+VG ≥150 minutes/week AND ≥5 sessions W + M + (Vx2) ≥150 minutes/week AND ≥5 sessions Measure 3 150 mins and 5 sessions Measure 4 Inactivity Truncation rules Proportion reporting NO activity (≥10 minutes at a time) For each activity (walking, moderate, vigorous activity) weekly minutes truncated to a maximum of 840 minutes (2 hours per day or 14 hours per week). The sum of total weekly time in all activities truncated 1,680 minutes (4 hours per day or 28 hours per week). Notes: W = time spent walking; [W(t) = walking to/from places (AA); W(r) = walking for recreation or leisure (AA); W(all) = all walking (BRFSS and IPAQ); W(mv) = moderate and vigorous paced walking (IPAQ)]. M = time spent in moderate intensity activities. V = time spent in vigorous activities. 2004 VOL. 28 NO. 2 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Brown et al. Article differences in the individual items asked in each survey (see Table 1). For example, in the NHS, the number of minutes and sessions reported in the last two weeks was divided by two to give weekly times/sessions. In some cases, more than one interpretation of each measure was derived. For example, in the AA survey, one interpretation of the first three measures did not include time spent in “gardening or heavy yardwork” [four item AA (AA4)], while a second interpretation did [five item AA (AA5)]. Similarly, for the BRFSS, one interpretation included time spent in an additional walking question [three item BRFSS (BRFSS3)], while the second only included walking as part of the moderate intensity question [two item BRFSS (BRFSS2)]. For IPAQ, the first three measures were calculated (a) including all paces of walking (IPAQ) and (b) including only walking reported to be at moderate or vigorous pace (IPAQmv). These variations are summarised in Table 1. Note that for the AA survey, the walking question was split into two (walking ‘to and from places’ and ‘for recreation or pleasure’) and the responses were summed. Table 2: Numbers of participants in each age and sex group who completed each pair of surveys. Active Australia and NHS 18-44 years Men Women 45-59 years Men Women 60-75 years Men Women Total 112 119 42 45 47 63 428 Active Australia and BRFSS Active Australia and IPAC ducted using SAS version 8.02 (SAS Institute Inc., Cary NC, USA 1999-2001). Statistical analyses Means and quartiles were calculated for total time in activity derived from each survey and for the total number of days/ sessions of reported activity. Differences between the three pairs of measures were computed and displayed graphically using mean and difference plots.8 For the three categorical measures, ‘per cent agreement’ was calculated for both measures of ‘sufficiently active’ (150 minutes, and 150 minutes and five sessions) and for ‘sedentariness’. The consistency with which participants were classified as ‘sufficiently active’ or ‘insufficiently active’ and as ‘sedentary’ or ‘not-sedentary’ on each survey, correcting for chance agreement, was also assessed using Cohen’s Kappa.9 All analyses were con- Results Participants The overall response rate was 51%. Of the 1,280 participants, 428 answered the Active Australia and NHS surveys, 427 answered the AA and BRFSS and 425 answered the AA and IPAQ surveys. There was a similar distribution of men and women in each of three age groups in each survey group (see Table 2). Their education levels were similar to those reported for a random Queensland sample in 2001, with 39% having fewer than 12 years of education (37% in the Queensland sample), 18% having completed year 12 (19%), 24% with a trade or similar qualification (26%) and 19% with a diploma or degree (18%).10 The Table 3: Means and quartiles for total time and frequency of activity derived from each survey. Comparisons of measures AA4 AA5 NHS AA4 AA5 BRFSS2 BRFSS3 AA4 AA5 IPAQ IPAQmv Total time (weekly reported minutes) and distributional quartiles (minutes) Mean (SE) 25% 50% 75% 327 (18.4) 406 (19.8) 303 (17.4) 317 (16.8) 399 (19.9) 461 (21.1) 761 (27.4) 353 (18.9) 450 (20.8) 918 (27.9) 856 (28.1) 60 100 36 40 90 90 240 53 95 430 360 180 270 180 210 253 310 720 210 300 870 840 480 600 428 480 590 840 1180 585 720 1500 1380 Frequency (days/sessionsa) and quartiles (days) Mean (SE) 25% 50% 75% 5.9 (6.5) 6.6 (6.6) 4.6 (4.9) 5.5 6.4 5.0 8.9 5.3 6.4 8.8 8.2 (5.2) (5.6) (4.5) (6.1) (4.9) (5.2) (5.8) (5.9) 1 2 1 2 2 2 5 2 2 4 3 4 5 3 5 5 5 9 4 5 8 7 8 9 6.5 7 9 7 12 8 9 13 12 Notes: (a) Note that more than 7 sessions/days can be accrued per week, by summing across walking, moderate and vigorous questions. AA4 = four item Active Australia (both walking questions, moderate and vigorous activities, not including gardening). AA5 = five item Active Australia (both walking questions, moderate and vigorous activities and gardening). NHS= National Health Survey, walking, moderate and vigorous. BRFSS2 = two item BRFSS, moderate and vigorous activities only. BRFSS3= three item BRFSS, including walking, moderate and vigorous activities. IPAQ = all paces of walking, plus moderate and vigorous activities. IPAQmv = only moderate and vigorous paced walking, and other moderate and vigorous activities. SE = standard error. AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2004 VOL. 28 NO. 2 Methods Comparison of PA surveys respondents were similar to the Australian population in terms of the proportion categorised as ‘adequately active for health benefit’ on the AA survey (43.2% of this sample and 45.2% nationally). Prevalence data – ‘sufficient physical activity’ Measures of agreement for the prevalence of ‘sufficiently active’ and ‘sedentariness’ from the three pairs of surveys are shown in Table 4. This table shows the proportions meeting the 150minute criterion (top panel), the proportions meeting both the 150 minutes and f ive days/sessions criteria (middle panel), and the proportions reporting no activity (bottom panel). Per cent agreement coefficients and kappa coefficients with 95% confidence intervals are shown for the paired data in each row. The f irst row of data shows that prevalence estimates from AA and NHS were similar, especially when AA4 data were used. Compared with AA 4, prevalence was about 10% higher when BRFSS data were used. However, there was closer agreement between prevalence estimates from BRFSS and AA5, but the Kappa scores were in the modest range. When walking was ‘double counted’ in the five item BRFSS, prevalence estimates were much higher but the per cent agreement and Kappa scores were not markedly changed. The relationship between the AA and the short IPAQ questionnaire indicates that use of the IPAQ survey resulted in much higher prevalence estimates than the AA instrument, across all modes of measurement. For example, there was a prevalence difference of around 26% between the AA 4 and the short IPAQ on the criterion of 150 minutes per week. When the 150 minutes and f ive sessions criteria were used, the relationships between the three pairs of surveys were similar to those described above, but the prevalence estimates were between 13% and 19% lower than when the single 150 minutes criterion was used (see Table 4, middle panel). Total time and number of days/sessions Means and quartiles for total activity time and for frequency of days/sessions reported for each pair of surveys are shown in Table 3. The difference in mean total activity time between the NHS and the four item AA survey (AA4, without vigorous yard work or gardening) was 24 minutes (SE:17). When the AA survey was compared with the BRFSS, the differences were much larger (see middle panel of Table 3). The BRFSS total from the moderate and vigorous questions, without the additional ‘double counted’ walking question, was 144 (SE:21) minutes more than the AA 4 total. However, when the time spent in gardening item was added to the AA total (AA5) the mean difference was only 62 (SE:21) minutes. The addition of the BRFSS ‘walking question’ increased the total time estimate by 362 or 444 minutes when compared with AA5 or AA 4 respectively. The differences in mean total time from the AA and short IPAQ surveys are shown in the bottom panel of Table 3. When only vigorous and moderately paced walking time was included in the IPAQ total, the difference (compared with AA5) was 468 (SE:27) minutes, and when all walking was included in the IPAQ total the difference was 406 (SE:27) minutes. Differences between these two surveys amounted to more than 500 minutes per week when AA 4 results were used. These differences between the times reported in the AA4 and the other three surveys are illustrated graphically using Bland and Altman plots in Figure 1. From these, it is clear that there was reasonable agreement between the AA 4 and NHS surveys (mean difference close to zero), but the funnel shape that is evident in all three graphs indicates that absolute agreement worsened as the average time reported increased. Given that most of the health benef its of PA are seen with PA durations of up to one hour per day (about 400 minutes per week), it is of less concern in terms of PA measurement that the poorest agreement was seen for levels of about 800 minutes per week. The same pattern was evident for the other two comparisons, but with a much larger mean difference for the IPAQmv and AA4 comparison. The data in Table 3 also show the mean number of times (AA, NHS) or days (IPAQ, BRFSS) reported in each pair of surveys. The patterns of difference between the surveys were similar to those described for total minutes (above), with the lowest frequency reported for the NHS, and highest for the BRFSS and IPAQ. Analysis of the order of survey administration found very little ordering effect of the questions in the comparisons between AA and both NHS and BRFSS. However, in the AA and IPAQ comparison, there was a trend for AA to score more total minutes and number of days/sessions when IPAQ was asked first, compared with the results when AA was asked first, but the trend was not statistically significant (data not shown). 2004 VOL. 28 NO. 2 Prevalence data – sedentariness The data in the lower panel of Table 4 show that, in general, the more items included in each version of each survey, the lower the prevalence of sedentariness, with overall estimates of sedentariness higher when the AA, NHS and two item BRFSS were used. Per cent agreement scores were higher than those shown for ‘activity’ but Kappa scores were lower for sedentariness than for ‘activity’ in the AA/NHF and AA/BRFSS comparisons. Discussion The aim of this study was to compare agreement between prevalence estimates for ‘sufficient activity’ derived from four survey instruments, using a randomly selected population sample. The AA survey was used as a ‘reference’ as it is in current population use for PA surveillance in Australia. The comparison instruments were the ‘traditional’ Australian NHS measure, the US BRFSS, and the recently developed IPAQ. The f indings clearly demonstrated that there were large differences in the reported PA times and hence in the prevalence estimates of ‘sufficient activity’ from these four measures. The highest level of agreement was between the AA and NHS and the poorest was between the AA and IPAQ. This reflects the different ‘domains’ of activity included in each survey. Traditionally, PA surveys have focused on leisure-time PA (LTPA), because, until the mid 1990s, the health benefits of PA were largely attributed to AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Brown et al. Article Figure 1a-c: Plots of differences in total weekly minutes for pairs of comparison surveys (y axis), against the average time reported in the two surveys (x axis). 1a: comparison of NHS v AA4; 1b: comparison of BRFSS2 v AA4; 1c: comparison of IPAQmv v AA4. Figure 1a Weekly minutes (NHS, AA4) Difference in minutes (NHS-AA4) Average in minutes (NHS and AA4) Figure 1b Weekly minutes (BRFSS2, AA4) Difference in minutes (BRFSS2 -AA4 ) Average in minutes (BRFSS2 and AA4) Figure 1c Weekly minutes (IPAQmv, AA 4) Difference in minutes (IPAQmv-AA4) Average in minutes (IPAQmv and AA4) AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2004 VOL. 28 NO. 2 Methods Comparison of PA surveys participation in more vigorous forms of activity such as organised sport and fitness. More recently, as interest in the obesity epidemic has focused our attention on total energy expenditure, there have been attempts to include different domains of activity, such as transport and occupational activity, in PA surveys.1 In some cultures, energy expended in work and transport contributes much more to total energy expenditure than LTPA, and the IPAQ survey probably does best at ‘capturing’ activity in all these domains. As a result, the minutes of PA reported in response to the IPAQ survey are higher than for the other three surveys, and prevalence estimates are concomitantly higher. This has implications for policy, as prevalence estimates are used to derive the population attributable risks of behaviours, which are in turn used to determine priority areas for public health action. For example, using the NHS, AA 4, and BRFSS2 we would estimate that about half the population is not sufficiently active for health benef it, compared with 20-30% using IPAQ. More research into the relative health benefits of activity in each PA domain is required to assess whether the ‘threshold’ for categorising ‘activity’ should be changed if more domains are included, and criterion-based validity data are urgently required for all four of these surveys. One contributing factor to the higher times reported in the IPAQ may be that this survey was the only one of the four to ask respondents to think about a ‘usual’ week. While this will overcome any problems relating to the fact that the ‘last week’ may be Table 4: Per cent agreement and Kappa scores for the proportion of participants categorised as ‘sufficiently active’ (a) using the criterion of 150 minutes/week (top panel), (b) using the criterion of 150 minutes and 5 sessions/week (middle panel), and (c) for the proportion of participants categorised as ‘sedentary’ (no physical activity of any kind reported, bottom panel) for each pair of surveys. Active Australia (a) 150 min/week AA4 Alternative NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv NHS BRFSS2 BRFSS3 IPAQ IPAQ mv AA prevalence Alternative prevalence % agreement Kappa (95% CI) 0.50 0.34 0.26 0.31 0.32 0.44 0.35 0.29 0.40 0.41 0.47 0.36 0.24 0.35 0.37 0.40 0.38 0.26 0.45 0.46 0.41 0.26 0.25 0.31 0.37 0.30 0.21 0.26 0.36 0.45 (0.42-0.58) (0.25-0.43) (0.18-0.34) (0.23-0.39) (0.24-0.40) (0.35-0.52) (0.26-0.45) (0.20-0.38) (0.30-0.49) (0.31-0.50) (0.38-0.55) (0.27-0.45) (0.17-0.31) (0.28-0.42) (0.29-0.44) (0.31-0.48) (0.29-0.47) (0.18-0.35) (0.37-0.53) (0.37-0.54) (0.29-0.52) (0.14-0.37) (0.13-0.37) (0.18-0.43) (0.24-0.50) (0.19-0.42) (0.09-0.33) (0.11-0.40) (0.20-0.52) (0.30-0.60) AA5 (b) 150 min/week PLUS 5 sessions AA4 AA5 (c) Sedentary AA4 AA5 Notes: AA4 = four item Active Australia (both walking questions, moderate and vigorous activities, not including gardening). AA5 = five item Active Australia (both walking questions, moderate and vigorous activities and gardening). NHS= National Health Survey, walking, moderate and vigorous activities. BRFSS2 = two item BRFSS, moderate and vigorous activities only. BRFSS3= three item BRFSS, including walking, moderate and vigorous activities. IPAQ = all paces of walking, plus moderate and vigorous activities. IPAQmv = only moderate and vigorous paced walking, and other moderate and vigorous activities. CI = confidence interval 2004 VOL. 28 NO. 2 AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH Brown et al. Article atypical due to illness or holidays, it is likely that this form of questioning will result in more socially acceptable, and therefore more inflated responses. It may also be true that between survey differences are attributable in part to the assessment of activity duration. Notably, the BRFSS and the IPAQ require respondents to estimate the amount of time spent in each activity domain on a single day. In contrast, the AA and NHS ask respondents to estimate the time spent in each activity domain for the entire recall period. Given that physical activity behaviour exhibits considerable day-to-day variability,4,11 it is possible that estimating the ‘usual’ or ‘average’ duration of activity on a single day may be inherently more difficult for respondents than recalling the duration of each activity session performed and summing over the entire recall period. One of the strengths of this study was that we used a randomly selected population sample with PA patterns similar to those previously reported in Australia.2 A limitation of the study was that participants were asked to respond to two surveys on one occasion, and their responses to one survey may have influenced their responses to the other. However, the order of administration of the surveys did not greatly affect the results. Overall, this study has demonstrated the difficulty of intersurvey comparison when surveys are designed to include different domains of physical activity. Each survey ‘captures’ different dimensions of total physical activity, ranging from the relatively narrow leisure time PA focus of the NHS to the more inclusive IPAQ survey, which attempts to have respondents think about all types of daily activity at work, at home and during recreation. Given that the variability between methods does not show consistent patterns, it is not possible to develop algorithms to translate prevalence estimates obtained from different surveys. In light of this, and of the public health need to track trends in PA over time, it is important to consistently use the same survey for population monitoring purposes. In Australia, the NHS items have been used by the ABS since 1985, but prevalence estimates are lower than for the other three surveys because of the focus on more ‘structured’ leisure-time activities. The AA survey was developed with a view to capturing more of the ‘moderate intensity’ activity associated with today’s lifestyle. As it has now been used three times in national surveys and as it appears to perform as well as any of the available alternatives, its continued use for population surveys is recommended so that trend data over a longer period of time can be established. The IPAQ survey may be useful for evaluation of intervention trials, when more details about changes in different domains of physical activity are required. Acknowledgements This work was supported by a grant from the Australian Commonwealth Department of Health and Ageing.

Journal

Australian and New Zealand Journal of Public HealthWiley

Published: Apr 1, 2004

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