Abstract
Purpose
Few physical activity (PA) questionnaires were designed to measure the lifestyles and activities of women. We sought to examine the test-retest reliability of a PA questionnaire used in the Women's Health Initiative (WHI) Study. Differences in reliability were also explored by important covariates.
Methods
Participants (n=1092) were post-menopausal women aged 50-79 years, randomly selected from the baseline sample of participants in the WHI Observational Study. The WHI physical activity questionnaire collects usual frequency, duration, and pace of recreational walking, frequency and duration of other recreational activities or exercises (mild, moderate and strenuous), household, and yard activities. Approximately half of the women (n=569) repeated questions on recreational PA, the other half (n=523) repeated questions related to household and yard activities (mean 3 months apart). Test-retest reliability was assessed with kappa and intraclass correlation coefficients (ICC1,1).
Results
Overall, questions on recreational walking, moderate recreational PA, and strenuous recreational PA had higher test-retest reliability (weighted kappa range 0.50-0.60), than questions on mild recreational PA (weighted kappa range 0.35-0.50). The ICC1,1 for moderate to strenuous recreational PA was 0.77 (95% CI 0.73, 0.80) and total recreational PA was 0.76 (95% CI 0.71, 0.79). Substantial reliability was observed for the summary measures of yard activities (ICC1,1 0.71; 95% CI 0.66, 0.75) and household activities (ICC1,1 0.60, 95% CI 0.55, 0.66). No meaningful differences were observed by race/ethnicity, age, time between test and retest, and amount of reported PA.
Conclusions
The WHI PA questionnaire demonstrated moderate to substantial test-retest reliability in a diverse sample of post-menopausal women.
Keywords: Epidemiology, movement, reproducibility, women's health, exercise
Introduction
Paragraph 1 Understanding physical activity and its on impact on health is an important public health challenge (35). Nearly half of the American population does not engage in enough physical activity to prevent disease or benefit health (9). Compared to men, women participate in less vigorous leisure activity (7, 8) and may engage in more sedentary behaviors (8, 24). Furthermore, previous studies have indicated that minority women report even less leisure time physical activity than white women (7, 8, 25, 35). Additional research on physical activity behaviors in women and minority populations would help guide public health policy and interventions.
Paragraph 2 Previous research demonstrates that women engage in different types and patterns of physical activity than men (2, 3, 34). Women may have a different interpretation or understanding of what physical activity means to them (2, 14, 15, 21, 30, 34). Because many physical activity questionnaires used in epidemiologic research were originally designed for white male populations, they may not accurately measure physical activity in women (2, 21, 33). This makes accurate and reliable measurement of physical activity in women and minority populations especially challenging. Additionally, few physical activity questionnaires have detailed measurement properties reported among minority or other special populations of women. Furthermore, the validity and reliability of physical activity questionnaires may be impacted by other attributes such as age, length of time between test and retest, or level of physical activity. These attributes may affect the ability of individuals to remember, comprehend, and answer questions.
Paragraph 3 One study that has attempted to address issues of physical activity measurement in women is the Women's Health Initiative (WHI) Observational Study. The WHI is a long-term, multi-center, racially and ethnically diverse national cohort study of 161,808 women. The WHI enables scientists to study relationships between lifestyle, health risk factors, and specific disease outcomes. To date, over 230 papers have been published using WHI data. Several of these papers have explored the associations of physical activity with major diseases (10, 16, 20, 22, 23). In order to adequately study risk factors, like physical activity, it is important for researchers to understand the questionnaires' measurement properties. The objective of this paper is to examine the test-retest reliability of the WHI physical activity questionnaire in a random sample of the WHI participants overall and by race/ethnicity, age, time between test and retest, and level of physical activity.
Methods
Paragraph 4 Between 1994 and 1998, over 93,676 women between 50 and 79 years of age were enrolled at one of 40 clinic centers across the United States into the WHI Observational Study (19). Eligibility for enrollment included the intention to reside in the area for at least three years, free from any major medical condition which would impact survival within three years of study entry, and no reported mental illness, dementia, alcoholism, or drug dependency. Full details on the study cohort and design are available elsewhere (19).
Paragraph 5 Between October 1996 and June 1997, a sub-sample of the women enrolled in the WHI Observational Study was selected to participate in the Measurement and Precision Study. Participants (n=1,092) were randomly recruited within the 40 clinic centers and stratified by age and race/ethnicity (American Indian/Alaskan Native, Asian or Pacific Islander, Black or African American, Hispanic/Latino, White).
Paragraph 6 The purpose of the Measurement and Precision Study was to assess test-retest reliability of several self-administered questionnaires. Each clinic center was randomly assigned to repeat a set of baseline questionnaires (19). At approximately 12-week intervals (range: 8-15 weeks), half of the women (n=567) repeated questions on exercise/recreational activities (Form 34) and the other half (n=512) repeated questions related to household, yard, and sedentary activities (Form 42). The two questionnaires were distributed between the samples in order to reduce the time burden on the participants. The 12 week time interval (8-15 weeks) was chosen to minimize a “learned” response to the instrument, so participants would not recall their previous answers. Institutional Review Board approval was obtained by each participating WHI center prior to data collection and participants provided their written informed consent.
Physical Activity Questionnaire
Paragraph 7 The physical activity questionnaire was self-administered at enrollment. The questionnaire was intentionally worded without reference to a specific time frame (e.g, last week, last month, last year), in order to collect “usual” activity or patterns of activity. It was designed to collect different types of activities by grouping them together by intensity. This was done to reduce the burden and time needed to complete the questionnaire. The questionnaire was divided into two forms to collect information on usual physical activity. On the first form, participants reported their usual exercise or recreational activity (mild, moderate, strenuous, and walking activities). On the second form, participants were asked about heavy indoor household activities and yard activities. Both forms were completed at the same time, either at the clinics or mailed to the participant, and then returned to the clinic for review.
Paragraph 8 The questionnaire grouped exercise or recreational activities into three separate intensities (mild, moderate, and strenuous) based a range of metabolic equivalent (MET) values associated with the type of activities described. The participants then reported the usual frequency (6 categories, from 0 to 5+ days per week) and duration (4 categories, from < 20 minutes to ≥ 60 minutes) of activities performed at each intensity level. Episodes of walking outside of the home (10 minutes or more) were reported separately through frequency (6 levels, 0 to 7 days per week), duration (4 levels, <20 minutes to ≥60 minutes), and usual speed (4 levels, 2 mph to 5 mph). Questions on household activities were assessed as hours per week (5 categories, from <1 hour to ≥10 hours). Yard activities included the number of months per year (5 categories, <1 month to ≥10 months) and hours per week (5 categories, <1 hour to ≥10 hours) the activities were performed. Participants were also asked to report number of hours spent sitting and lying down, including sleep, each day (8 categories, <4 hours to ≥16 hours). In addition, the women were also asked to recall whether or not they engaged in strenuous activity (yes or no) at 18, 35, and 50 years of age. The questionnaire and scoring protocol can be found in Appendix 1.
Paragraph 9 The WHI physical activity measures were designed to be summarized into continuous variables estimating weekly energy expenditure (MET-hours per week) from each type of activity (mild, moderate, strenuous, walking, household, and yard). An estimated MET level for each type of activity was assigned from a compendium of activities (1) (Appendix 2), where the MET level is kilocalories per kilogram of body weight expended each hour during a specific activity. Summary variables were created by combining frequency, duration and MET-estimated intensity in the following equation: [(Frequency of activity per week × Minutes per session × MET for that activity) / (60 min/hour)]. These summary variables in “MET-hours” quantify the total kilocalories expended per kilogram per week. MET units are independent of body weight.
Socio-demographic Measures
Paragraph 10 Participants answered questions on a number of important health behaviors and demographic attributes. Race/ethnicity (American Indian/Alaskan Native, Asian or Pacific Islander, Black or African American, Hispanic/Latino, White), education (10 levels), main occupation (professional/managerial, technical/sales/administrative, service/labor, homemaker), retirement status, martial status, smoking status, and general health were all self-reported at the first clinic visit. Additionally height and weight for each individual were measured at this visit and used to calculate body mass index (BMI) (weight in kilograms divided by height in meters squared), and categorized as underweight (<18.5 kg/m2), normal weight (18.5-<25 kg/m2), overweight (25- <30 kg/m2), and obese (≥30 kg/m2) (37).
Statistical Analysis
Paragraph 11 Two-level kappa and weighted kappa (3-8 levels) statistics were used to assess the test-retest reliability of each individual question or corresponding component (e.g., frequency, duration). Weighting for the kappa statistics was applied using the default in SAS, the Cicchetti-Allison form, taking into account the degree of non-agreement between the test and retest. Agreement between the test and retest were categorized into five categories: poor (0 to < 0.2), fair (0.2 to < 0.4), moderate (0.4 to < 0.6), substantial (0.6 to < 0.8), and almost perfect (0.8 to 1.0) (18). Test-retest reliability of the continuous variables was assessed with the Shrout and Fleiss intraclass correlations coefficient (ICC1,1) (29) . This ICC1,1 uses test and retest measures to estimate single trial reliability, instead of the average of repeated measures. More specifically the ICC1,1 and 95% confidence intervals were calculated using a one-way analysis of variance model (ANOVA) (29, 31, 32) and assessed the proportion of the total variance (true variability and measurement error) that was attributable to participant variability.
Paragraph 12 Stratified analyses were performed by race/ethnicity, time between test and retest (<=3 months vs. >3 months), age (50 - ≤65 years, > 65 - 79 years), and by level of recreational activity (one or more episodes vs. none). Lastly, because the participants were not randomized to the type of activity form (exercise/recreation form vs. household/yard form), differences between the two samples were also examined.
Results
Study Sample
Paragraph 13 The majority of the sample (n=1092) reported good, very good, or excellent health (90%) and the average age was 64 years old (Table 1). The population was predominantly White (66%) followed by Hispanic (14%), African American (13%), and Asian/Pacific Islander (7%). Only 1% of the women identified themselves as American Indian/Alaskan Natives. These women were excluded from the racially stratified analysis only because of inadequate sample size. Most women had completed high school (93%) and reported an occupation (current or former) other than being a homemaker (90%). More than half of them (55%) were retired. Approximately half of the sample (51%) reported never smoking and more than half (57%) were overweight or obese. The majority of the women were married, while onethird were either widowed, separated, or divorced.
Table 1.
Socio-demographic description of participants in the WHI Measurement and Precision Study at the first clinic visit (n=1092)
| N | % | |
|---|---|---|
| Education | ||
| Less than high school | 75 | 6.9 |
| High school | 197 | 18.2 |
| Some college or vocational/associates | 406 | 37.6 |
| College degree | 402 | 37.2 |
| Race/Ethnicity | ||
| American Indian or Alaskan Native | 13 | 1.2 |
| Asian or Pacific Islander | 74 | 6.8 |
| Black or African-American | 138 | 12.6 |
| Hispanic/Latino | 148 | 13.6 |
| White | 719 | 65.8 |
| General Health | ||
| Excellent | 178 | 16.4 |
| Very good | 421 | 38.8 |
| Good | 382 | 35.2 |
| Fair | 91 | 8.4 |
| Poor | 14 | 1.3 |
| Occupation | ||
| Managerial / Professional | 415 | 39.3 |
| Technical / Sales / Administrative | 340 | 32.2 |
| Service/Labor | 190 | 18.0 |
| Homemaker | 110 | 10.4 |
| Retired | ||
| No | 487 | 45.0 |
| Yes | 596 | 55.0 |
| Marital status | ||
| Never married | 52 | 4.8 |
| Divorced, separated or widowed | 345 | 31.7 |
| Presently married or marriage-like relationship | 680 | 63.5 |
| Body mass index | ||
| Underweight | 31 | 2.8 |
| Normal | 433 | 39.7 |
| Overweight | 360 | 32.0 |
| Obese | 268 | 24.5 |
| Smoking | ||
| Never | 553 | 51.3 |
| Former | 458 | 42.5 |
| Current | 67 | 6.2 |
| Total exercise and recreational activity | ||
| No exercise or recreational activity | 50 | 8.9 |
| Some activity of limited duration or frequency | 254 | 45.4 |
| 2 to <4 episodes per week | 108 | 19.3 |
| 4 or more episodes per week | 148 | 26.4 |
Paragraph 14 Although participants were randomly chosen from within each center, each center was assigned to only one of the two physical activity forms (exercise/recreational activity vs. yard/household). Several differences in the populations were found between the two forms. Differences of 5% or more were observed between the two samples for the following variables: race/ethnicity, education, and BMI. A greater proportion of the participants who answered the questionnaire on exercise/recreation activities were normal weight (43% vs. 36%), White (69% vs. 63%), and college graduates (40% vs. 34%), compared to the sample that answered the questions on household/yard activities. Differences were not observed between general health, occupational status, marital status, and smoking.
Paragraph 15 At baseline, 73% of the women were not strenuously active, and more than half had not participated in regular strenuous activity in their earlier adulthood (ages 18, 35, 50 years) (data not shown). At least 80% of the women reported some walking. However, when all exercise was combined, fewer than half of the women reported fewer than 10 MET-hours per week (median 9.0 MET-hours/week, S.D. 14.3). Whites and Asian/Pacific Islanders had higher median levels of total recreational activity than Hispanic and African Americans (9.8, 8.7, 7.5, 7.5 MET-hours/week, respectively). A similar pattern was observed for strenuous recreational activity and moderate to strenuous recreational activity by race/ethnicity (data not shown). More women reported at least one episode of moderate recreational activity (e.g., easy swimming, biking, or dancing) than mild recreational activity (e.g., bowling or golf) (Table 2).
Table 2.
Description of physical activity at the first clinic visit, among participants of the WHI Measurement and Precision Study
| Variable | N | Mean | Median | SD | Missing |
|---|---|---|---|---|---|
| Form 34: Exercise or recreational physical activity (n=569) | |||||
| Mild recreational physical activity (MET-hours/week) | 551 | 1.2 | 0 | 2.6 | 18 |
| Moderate recreational physical activity (MET-hours/week) | 553 | 3.2 | 0 | 5.1 | 16 |
| Vigorous recreational physical activity (MET-hours/week) | 562 | 4.0 | 0 | 9.0 | 7 |
| Walking recreational physical activity (MET-hours/week) | 563 | 4.9 | 2.5 | 6.2 | 6 |
| Moderate to strenuous recreational physical activity (MET-hours/week | 544 | 9.8 | 4.5 | 13.2 | 25 |
| Total recreational physical activity (MET-hours/week) | 526 | 13.3 | 9.0 | 14.3 | 43 |
| Form 42: Household and yard physical activity (n=523) | |||||
| Household physical activity (MET-hours/week) | 518 | 7.7 | 7.0 | 9.1 | 5 |
| Yard physical activity (MET-hours/week) | 515 | 3.8 | 0 | 6.8 | 8 |
| Sitting and lying down (hours per week) | 519 | 14.5 | 15.0 | 4.3 | 4 |
Test-retest Reliability
Paragraph 16 Within the entire sample, substantial test-retest reliability was demonstrated in most summary measures, with the exception of mild recreational activity, which had lower reliability (Table 3). The continuous estimate of total physical activity (ICC1,1) was 0.76 (95% CI 0.71, 0.79) and the categorical estimate of total physical activity (weighted kappa) was 0.61 (95% CI 0.56, 0.66) (Tables 3 and 4).
Table 3.
Intraclass correlation coefficients (ICC1,1) and 95% confidence intervals (CI) of physical activity measures overall and among women who reported recreational activity in the WHI Measurement and Precision Study
| Entire sample | Women with ≥1 episode of recreational physical activity# | |||
|---|---|---|---|---|
| ICC1,1 | 95% CI | ICC1,1 | 95% CI | |
| Form 34: Exercise or recreational physical activity | n=569 | n=310 | ||
| Mild recreational physical activity (MET-hours/week) | 0.51 | 0.45, 0.57 | 0.55 | 0.47, 0.62 |
| Moderate recreational physical activity (MET-hours/week) | 0.57 | 0.52, 0.63 | 0.60 | 0.53, 0.67 |
| Strenuous recreational physical activity (MET-hours/week) | 0.76 | 0.73, 0.80 | 0.76 | 0.71,0.80 |
| Walking recreational physical activity (MET-hours/week) | 0.75 | 0.72, 0.79 | 0.71 | 0.65, 0.76 |
| Moderate to strenuous recreational physical activity (MET-hours/week) | 0.77 | 0.73, 0.80 | 0.74 | 0.68, 0.78 |
| Total recreational physical activity (MET-hours/week) | 0.76 | 0.71, 0.79 | 0.73 | 0.67, 0.77 |
| Form 42: Household and yard physical activity | n=523 | |||
| Household physical activity (MET-hours/week) | 0.60 | 0.55, 0.66 | N/A* | |
| Yard physical activity (MET-hours/week) | 0.71 | 0.66, 0.75 | ||
| Sitting and lying down (hours per week) | 0.60 | 0.54, 0.65 | ||
Only applicable for women who completed the recreational physical activity form
One episode of any recreational physical activity, regardless of intensity or duration
Table 4.
Kappa statistics and 95% confidence intervals (CI) of the physical activity components measures overall and among women who reported recreational activity in the WHI Measurement and Precision Study
| Entire sample | Women with ≥1 episode of recreational activity# | |||||
|---|---|---|---|---|---|---|
| N | Weighted Kappa | 95% CI | N | Weighted Kappa | 95% CI | |
| Form 34: Exercise or recreational physical activity | ||||||
| Mild physical activity, days per week | 548 | 0.36 | 0.27, 0.45 | 303 | 0.40 | 0.28, 0.51 |
| Mild physical activity, minutes per session | 528 | 0.52 | 0.43, 0.61 | 295 | 0.51 | 0.40, 0.62 |
| Moderate physical activity, days per week | 563 | 0.53 | 0.47, 0.59 | 314 | 0.54 | 0.47, 0.47 |
| Moderate physical activity, minutes per session | 544 | 0.48 | 0.41, 0.54 | 297 | 0.44 | 0.36, 0.53 |
| Strenuous physical activity, days per week | 555 | 0.62 | 0.55, 0.68 | 314 | 0.62 | 0.55, 0.69 |
| Strenuous physical activity, minutes per session | 546 | 0.61 | 0.54, 0.68 | 306 | 0.60 | 0.52, 0.68 |
| Number of walks per week >= 10 minutes | 567 | 0.60 | 0.55, 0.65 | 314 | 0.55 | 0.48, 0.61 |
| Minutes per walk | 555 | 0.59 | 0.54, 0.65 | 307 | 0.59 | 0.52, 0.66 |
| Usual speed of walk | 556 | 0.60 | 0.54, 0.65 | 306 | 0.58 | 0.50, 0.66 |
| Total exercise and recreational activity exposure | 569 | 0.61 | 0.56, 0.66 | 314 | 0.51 | 0.42, 0.59 |
| Form 42: Household and yard physical activity | ||||||
| Heavy indoor chores hours per week | 517 | 0.52 | 0.45, 0.58 | N/A* | ||
| Yard work, months per year | 511 | 0.67 | 0.62, 0.71 | |||
| Yard work, hours per week | 509 | 0.64 | 0.59, 0.70 | |||
| Historical strenuous physical activity | ||||||
| Strenuous physical activity at age 18 years | 527 | 0.55** | 0.48, 0.63 | 288 | 0.57** | 0.47, 0.66 |
| Strenuous physical activity at age 35 years | 526 | 0.55** | 0.48, 0.63 | 294 | 0.55** | 0.45, 0.65 |
| Strenuous physical activity at age 50 years | 535 | 0.53** | 0.46, 0.60 | 301 | 0.53** | 0.44, 0.63 |
Only applicable for women who completed the recreational physical activity form
One episode of any recreational physical activity, regardless of intensity or duration
Simple kappa statistic
Paragraph 17 Reliability was similar when the sample was reduced to only those women who reported at least one episode of exercise or recreational activity (Table 3). Stratifying by race/ethnicity resulted in a loss of precision, but the associations were similar (Table 5). The exception was mild recreational activity which consistently demonstrated the lowest reliability, especially in non-white participants. When stratified by age, women who were <=65 years of age demonstrated higher reliability than women >65 years (Table 6). However the magnitude of these differences was small, as the measures in both strata remained similar to the reliability of the entire sample. Additionally, the population of women who repeated the tests within three months also tended to have slightly higher reliability compared to women for whom more than three months had passed at retest (Table 6).
Table 5.
Intraclass correlation coefficients (ICC1,1) and 95% confidence interval's (CI) of physical activity measures by race/ethnicity in the WHI Measurement and Precision Study
| White | African American | Hispanic | Asian/Pacific Islander | |||||
|---|---|---|---|---|---|---|---|---|
| ICC1,1 | 95% CI | ICC1,1 | 95% CI | ICC1,1 | 95% CI | ICC1,1 | 95% CI | |
| Form 34: Exercise or recreational physical activity | n=390 | n=60 | n=82 | n=35 | ||||
| Mild recreational physical activity (MET-hours/week) | 0.53 | 0.46, 0.60 | 0.07 | -0.19, 0.31 | 0.44 | 0.24, 0.59 | 0.66 | 0.60, 0.72 |
| Moderate recreational physical activity (MET-hours/week) | 0.77 | 0.72, 0.81 | 0.68 | 0.52, 0.79 | 0.82 | 0.74, 0.88 | 0.73 | 0.54, 0.86 |
| Strenuous recreational physical activity (MET-hours/week) | 0.74 | 0.69, 0.78 | 0.64 | 0.46, 0.77 | 0.92 | 0.88, 0.95 | 0.80 | 0.76, 0.84 |
| Walking recreational physical activity (MET-hours/week) | 0.75 | 0.70, 0.79 | 0.87 | 0.79, 0.92 | 0.69 | 0.56, 0.79 | 0.75 | 0.70, 0.79 |
| Moderate to strenuous recreational physical activity (MET-hours/week) | 0.77 | 0.72, 0.81 | 0.68 | 0.52, 0.79 | 0.82 | 0.74, 0.88 | 0.73 | 0.54, 0.86 |
| Total recreational physical activity (MET-hours/week) | 0.73 | 0.68, 0.77 | 0.72 | 0.58, 0.83 | 0.85 | 0.78, 0.90 | 0.78 | 0.74, 0.82 |
| Form 42: Household and yard physical activity | n=329 | n=78 | n=66 | n=39 | ||||
| Household physical activity (MET-hours/week) | 0.62 | 0.55, 0.68 | 0.65 | 0.50, 0.76 | 0.52 | 0.31, 0.67 | 0.77 | 0.60, 0.87 |
| Yard physical activity (MET-hours/week) | 0.78 | 0.73, 0.82 | 0.70 | 0.56, 0.80 | 0.31 | 0.07, 0.51 | 0.59 | 0.34, 0.76 |
| Sitting and lying down (hours per week) | 0.56 | 0.48, 0.63 | 0.66 | 0.52, 0.77 | 0.67 | 0.51, 0.78 | 0.54 | 0.28, 0.73 |
Table 6.
Intraclass correlation coefficients (ICC1,1) and 95% confidence interval's (CI) of physical activity measures by age and time between tests in the WHI Measurement and Precision Study
| <=65 years | >65 years | <= 3 months | >3 months | |||||
|---|---|---|---|---|---|---|---|---|
| ICC1,1 | 95% CI | ICC1,1 | 95% CI | ICC1,1 | 95% CI | ICC11,1 | 95% CI | |
| Form 34: Exercise or recreational physical activity | n=313 | n=256 | n=274 | n=295 | ||||
| Mild physical activity MET-hours per week | 0.66 | 0.59, 0.72 | 0.40 | 0.29, 0.50 | 0.60 | 0.51, 0.67 | 0.44 | 0.34, 0.52 |
| Moderate physical activity MET-hours per week | 0.59 | 0.51, 0.66 | 0.56 | 0.47, 0.64 | 0.57 | 0.48, 0.64 | 0.58 | 0.50, 0.65 |
| Strenuous physical activity MET-hours per week | 0.80 | 0.76, 0.84 | 0.71 | 0.64, 0.76 | 0.71 | 0.65, 0.77 | 0.80 | 0.76, 0.84 |
| Walking MET-hours per week | 0.75 | 0.70, 0.79 | 0.76 | 0.70, 0.80 | 0.84 | 0.81, 0.87 | 0.62 | 0.54, 0.68 |
| Moderate to strenuous recreational physical activity (MET-hours/week | 0.79 | 0.75, 0.83 | 0.73 | 0.67, 0.78 | 0.75 | 0.70, 0.80 | 0.78 | 0.74, 0.82 |
| Total recreational physical activity MET- hours per week | 0.78 | 0.74, 0.82 | 0.72 | 0.65, 0.77 | 0.76 | 0.70, 0.80 | 0.75 | 0.69, 0.79 |
| Form 42: Household and yard physical activity | n=288 | n=235 | n=274 | n=249 | ||||
| Household physical activity (MET-hours/week) | 0.65 | 0.58, 0.71 | 0.52 | 0.42, 0.61 | 0.60 | 0.55, 0.66 | 0.54 | 0.45, 0.62 |
| Yard physical activity (MET-hours/week) | 0.67 | 0.60, 0.73 | 0.77 | 0.72. 0.82 | 0.71 | 0.66, 0.75 | 0.66 | 0.58, 0.72 |
| Sitting and lying down (hours per week) | 0.68 | 0.62, 0.74 | 0.48 | 0.37, 0.57 | 0.60 | 0.54, 0.65 | 0.59 | 0.51, 0.67 |
Paragraph 18 In general, the reliability of the individual questions on the components of frequency and duration of exercise (strenuous, moderate, mild, and walking) was between 0.36 and 0.62 for the entire sample (Table 4). Better reliability was observed for the strenuous and walking components than moderate or mild components. The reliability estimates of hours spent sitting and lying down, as well as yard and indoor household activities ranged from 0.60 to 0.71 for the entire sample (Table 3).
Paragraph 19 History of strenuous activity at the ages of 18, 35, and 50 years, measured by kappa statistics, ranged between 0.53 to 0.55 overall (Table 4). Similar to the summary measures, reliability was not meaningfully influenced by restricting the analysis to only women who reported at least one episode of exercise or recreational activity. When stratified by the other relevant covariates (age, race/ethnicity, time between tests) the reliability of moderate, strenuous, and walking physical activity were all fair to moderate.
Discussion
Paragraph 20 The WHI Physical Activity Questionnaire demonstrated moderate to substantial test-retest reliability in a racially diverse sample of post-menopausal women. The reliability estimates observed in this sample are similar to reliability measures from other self-reported questionnaires designed for women (6) and for older adults (36). Additionally, the physical activity in this population generally paralleled activity patterns observed in the US population of adults (7, 8, 35).
Paragraph 21 The most consistent difference in the test-retest reliability estimates appeared to be lower reliability in the mild exercise or activity measures. Although it is possible that the lower reliability observed in the mild intensity questions may be an artifact of reduced precision, it is consistent with other research (27, 36). Activities of mild intensity are less memorable and less likely to be recalled, and are consequently less well captured by self-report questionnaires. Another potential explanation for the weaker performance of the mild activity measures may be a result of the questionnaire design. Mild walking, a popular recreational activity in this population, was assessed separately from other mild-intensity activities, and showed higher reliability than mild activity. Therefore, if walking had been included in the mild activity measure, instead of assessed separately, mild activity might have shown higher reliability.
Paragraph 22 Differences in test-retest reliability were not observed when reducing the sample to only women who reported at least one episode of any exercise or recreational activity. Interestingly, there were also no meaningful differences in reliability observed across race/ethnic groups. Previous studies have been mixed in their reporting of differences in reliability by race/ethnicity (5, 12, 28). However, it is also important to consider the wide confidence intervals in the race/ethnicity estimates, as stratifying the data resulted in a loss of precision.
Paragraph 23 Although we did not observe differences in reliability between the different race/ethnic groups, or by level of activity, some patterns were observed by age and length of time between test and retest. Women who were 65 years or younger demonstrated better test-retest reliability than women who were older. Variability of physical activity in older women may be influenced by a number of factors, such as changing health status, (e.g., fatigue, injury, disease progression), retirement, or loss of a spouse (4, 11, 13). Any of these changes within the study period could impact questionnaire reliability as women's activity patterns are affected. Additionally, aging is associated with cognitive decline that can impact memory and could in turn affect reliability (26).
Paragraph 24 Not surprisingly, a slightly higher pattern was observed in some measures among the sample of women who repeated tests within a three-month time period compared to women who experienced more than three months between the tests. One explanation could be because tests repeated within a shorter time frame are more likely to be given in the same season or comparable time of year with regards to weather. Furthermore, a change in activity (either increase or decrease) could have occurred after the administration of the first questionnaire, such that the reliability estimates would be lower.
Paragraph 25 While reliability could be explored with this data, validation of the WHI physical activity questionnaire could not be assessed. However, the questionnaire's validity was recently explored among 74 women enrolled in the Women's Healthy Eating and Living Study (17). In this convenience sample of women, the WHI physical activity questionnaire was correlated with both the accelerometer (Actigraph 7164) and 7-day physical activity recall (r=0.73, 0.88, respectively). Although the WHI questionnaire had 100% sensitivity for identifying women who met the physical activity guidelines, the specificity was only 60%. The questionnaire tended to underestimate moderate activities and overestimate vigorous activities.
Study Limitations
Paragraph 26 Despite the diverse and large sample, this study had several limitations. The WHI sample was not population-based and may not be representative of a specific source population. White women comprised a larger sample than other racial/ethnic groups. Because of the small sample sizes representing Hispanic, African American, and Asian/Pacific Islander women, the bounds of the lower confidence interval were estimated below zero in several of the stratified analyses. Additionally the level of education in our sample was very high and we were unable to examine variation in test-retest reliability by education. Another limitation to this study was that participants were not randomized to the two forms and some differences were observed between the two groups.
Paragraph 27 Several other considerations should be made when using the questionnaire. While the WHI physical activity assessment included a measure of yard and household activity, it was not a comprehensive measure of women's potential activities. Several domains of activity such as non-motorized transportation (active travel), child or elder care activity, and work or occupational physical activity were not included in the WHI physical activity questionnaire.
Conclusions
Paragraph 28 Reliable and valid questionnaires are a cost-effective and useful method for collecting physical activity information in large cohort studies, such as in the WHI Observational Study. However, measurement of physical activity is challenging as many questionnaires do not collect detailed information on types of activities and use terminology many women do not identify with (2, 21, 33, 34). The WHI Physical Activity Questionnaire is one of the first questionnaires to examine different types of physical activity in a large, multiethnic sample of women. This analysis shows that the different domains of physical activity behavior, such as recreational, yard, and household activity, can be reliably estimated in an ethnically diverse sample of post-menopausal women.
ACKNOWLEDGEMENTS
The WHI study was funded by the National Institutes of Health (NIH) / National Heart, Lung, and Blood Institute (NHLBI). This work was supported in part by the NIH/NHLBI #5-T32-HL007055. The results of the present study do not constitute endorsement by NIH or ACSM. The authors are also indebted to Drs. David Couper, Gerardo Heiss, Steve Marshall, and June Stevens, for their valuable feedback on the analysis and manuscript.
Appendix 1
Description and scoring of the WHI Physical Activity Questionnaire
| Questions | Response Options | Scoring |
|---|---|---|
| The following questions are about your usual physical activity and exercise. This includes walking and sports. | ||
| 1. Think about the walking you do outside the home. How often do you walk outside the home for more than 10 minutes without stopping? (Mark only one.) | Rarely or never | 0 - skip to #2 |
| 1-3 times each month | 0.5 times | |
| 1 time each week | 1.0 times | |
| 2-3 times each week | 2.5 times | |
| 4-6 times each week | 5.0 times | |
| 7 or more times each week | 7.0 times | |
| 1.1 When you walk outside the home for more than 10 minutes without stopping, for how many minutes do you usually walk? | Less than 20 minutes | 15 minutes |
| 20-39 minutes | 30 minutes | |
| 40-59 minutes | 50 minutes | |
| 1 hour or more | 70 minutes | |
| 1.2 What is your usual speed? | Casual strolling or walking (less than 2 miles an hour) | 2.0 METs |
| Average or normal (2-3 miles an hour) | 3.0 METs | |
| Fairly fast (3-4 miles an hour) | 4.0 METs | |
| Very fast (more than 4 miles an hour) | 5.0 METs | |
| Don't know | 2.0 (set to lowest MET intensity) | |
| Not including walking outside the home, how often each week (7 days) do you usually do the exercises below? | ||
| 2. STRENUOUS OR VERY HARD EXERCISE (You work up a sweat and your heart beats fast.) For example, aerobic dancing, jogging, tennis, wimming laps. | None | 0 - skip to #3 |
| 1 day per week | 1 times | |
| 2 days per week | 2 times | |
| 3 days per week | 3 times | |
| 4 days per week | 4 times | |
| 5 or more days per week | 6 times | |
| 2.1 How long do you usually exercise like this at one time? | Less than 20 minutes | 10 minutes |
| 20-39 minutes | 30 minutes | |
| 40-59 minutes | 50 minutes | |
| 1 hour or more | 70 minutes | |
| 3. MODERATE EXERCISE (Not exhausting). For example, biking outdoors, using an exercise machine (like a stationary bike or treadmill), calisthenics, easy swimming, popular or folk dancing. | None | 0 - skip to 4 |
| 1 day per week | 1 times | |
| 2 days per week | 2 times | |
| 3 days per week | 3 times | |
| 4 days per week | 4 times | |
| 5 or more days per week | 6 times | |
| 3.1 How long do you usually exercise like this at one time? | Less than 20 minutes | 10 minutes |
| 20-39 minutes | 30 minutes | |
| 40-59 minutes | 50 minutes | |
| 1 hour or more | 70 minutes | |
| 4. MILD EXERCISE. For example, slow dancing, bowling, golf. | None | 0--skip to 5.1 |
| 1 day per week | 1 times | |
| 2 days per week | 2 times | |
| 3 days per week | 3 times | |
| 4 days per week | 4 times | |
| 5 or more days per week | 6 times | |
| 4.1 How long do you usually exercise like this at one time? | Less than 20 minutes | 10 minutes |
| 20-39 minutes | 30 minutes | |
| 40-59 minutes | 50 minutes | |
| 1 hour or more | 70 minutes | |
| For each of the ages below, did you usually do strenuous or very hard exercises at least 3 times a week? This would include exercise that was long enough to work up a sweat and make your heart beat fast. (Be sure to mark "No" if you did not do very hard exercises at the ages listed below.) | ||
| 5.1 18 years old | No | 0 |
| Yes | 1 | |
| 5.2 35 years old | No | 0 |
| Yes | 1 | |
| 5.3 50 years old | No | 0 |
| Yes | 1 | |
| The next set of questions ask about some of your usual activities. | ||
| 6. About how many hours each week do you usually spend doing heavy (strenuous) indoor household chores such as scrubbing floors, sweeping, or vacuuming? | Less than 1 hour | 0 |
| 1-3 hours | 2.0 hours | |
| 4-6 hours | 5.0 hours | |
| 7-9 hours | 8.0 hours | |
| 10 or more hours | 12.0 hours | |
| 7. About how many months during the year do you usually do things in the yard, such as mowing, raking, gardening, or shoveling snow? | Less than 1 month | 0 |
| 1-3 months | 3.0 months | |
| 4-6 months | 5.0 months | |
| 7-9 months | 8.0 months | |
| 10 or more months | 11.0 months | |
| 7.1 When you do these things in the yard, how many hours each week do you do them? | Less than 1 hour | 0 |
| 1-3 hours | 2.0 hours | |
| 4-6 hours | 5.0 hours | |
| 7-9 hours | 8.0 hours | |
| 10 or more hours | 12.0 hours | |
| 8. During a usual day and night about how many hours do you spend sitting? Be sure to include the time you spend sitting at work, sitting at the table eating, driving or riding in a car or bus, and sitting up watching TV or talking. | Less than 4 hours | 2.0 hours |
| 4-5 hours | 4.5 hours | |
| 6-7 hours | 6.5 hours | |
| 8-9 hours | 8.5 hours | |
| 10-11 hours | 10.5 hours | |
| 12-13 hours | 12.5 hours | |
| 14-15 hours | 14.5 hours | |
| 16 or more hours | 16.5 hours | |
| 9. During a usual day and night about how many hours do you spend sleeping or lying down with your feet up? Be sure to include the time you spend sleeping or trying to sleep at night, resting or napping, and lying down watching TV. | Less than 4 hours | 2.0 hours |
| 4-5 hours | 4.5 hours | |
| 6-7 hours | 6.5 hours | |
| 8-9 hours | 8.5 hours | |
| 10-11 hours | 10.5 hours | |
| 12-13 hours | 12.5 hours | |
| 14-15 hours | 14.5 hours | |
| 16 or more hours | 16.5 hours | |
Appendix 2
Metabolic equivalent (MET) estimates*for intensity for each activity
| Activity | MET used in algorithm |
|---|---|
| Walking | |
| Casual | 2.0 |
| Average | 3.0 |
| Fast | 4.0 |
| Very Fast | 4.5 |
| Strenuous Exercise | 7.0 |
| Moderate Exercise | 4.5 |
| Light Exercise | 3.0 |
| Yard work | 4.0 |
| Housework | 3.5 |
based on Ainsworth, et al. (1)
Footnotes
Conflict of interest Dr. Morimoto works for Exponent in Menlo Park, CA.
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