PURPOSE:Physical activity (PA) diaries reduce the recall error inherent in self-reported PA but are burdensome. The purpose of this study was to compare a cell phone-based diary with a paper diary and examine the reliability and validity of the cell phone diary. METHODS:In a pilot study, 25 women and 23 men, age 45-65 yr, completed cell phone and paper PA diaries 4 d·wk(-1) for three consecutive weeks and a user satisfaction survey. In the subsequent validation study, 623 middle-age participants (52.5% women) were asked to complete the cell phone diary and wear an accelerometer for two 7-d periods, approximately 6 months apart. They also completed two PA questionnaires. Fitness, body mass index, and percent body fat were obtained as indirect validation criteria. RESULTS:Estimates of PA from the cell phone and paper diaries were similar (mean within person difference = -43.8 MET·min·d(-1) of total PA, SD = 360, P = 0.49, 7.4 min·d(-1) of moderate-vigorous PA, SD = 66, P = 0.53). Users preferred the cell phone diary over the paper diary (59.6% vs 35.4%). In the subsequent study, intraclass correlations for the cell phone diary ranged from 0.55 for light PA to 0.63 for vigorous PA. Although PA estimates from the cell phone diary were generally significantly higher than those from the accelerometer and the questionnaires, correlations for moderate and vigorous PA were moderate (ρ = 0.25-0.59 with the questionnaires and 0.27-0.35 with the accelerometer). The correlations between the cell phone diary and the indirect validation criteria were generally in the expected direction and of moderate magnitude. CONCLUSIONS:A cell phone-based PA diary is equivalent to a paper diary, acceptable to users, and a relatively reliable and valid approach to self-reported PA.

Purpose: To determine whether respondents share researchers' understandings of concepts and questions frequently used in the assessment of usual physical activity (PA) behavior. Methods: As part of On the Move, a study aimed at reducing measurement error in self-reported physical activity (PA), we conducted cognitive interviews with 19 men and 21 women, ages 45-65, regarding their responses to the PA questionnaires used in two large, population-based studies, Life After Cancer Epidemiology and California Men's Health study. One questionnaire asks about the frequency, the duration, and the perceived intensity of a range of specific activities in several different domains over the past 12 months. The second questionnaire asks about frequency and duration of specific, mostly recreational activities, grouped by intensity (i.e., moderate or vigorous) over the past 3 months. We used verbal probing techniques to allow respondents to describe their thought processes as they completed the questionnaires. All interviews were tape-recorded and transcribed, and the transcripts were then analyzed using standard qualitative methods. Results: Cognitive interviews demonstrated that a sizable number of respondents understood "intensity" in terms of emotional or psychological intensity rather than physical effort. As a result, the perceived intensity with which a participant reported doing a specific activity often bore little relationship to the MET value of that activity. Additionally, participants often counted the same activity more than once, overestimated work-related PA, and understood activities that were grouped together in a single category to be definitive lists rather than examples. Conclusion: Cognitive interviews revealed significant gaps between respondents' interpretations of some PA questions and researchers' assumptions about what those questions were intended to measure. Some sources of measurement error in self-reported PA may be minimized by additional research that focuses on the cognitive processes required to respond to PA questionnaires.

PURPOSE: To determine if respondents understand concepts and questions frequently used to assess usual physical activity behavior in the ways intended by researchers. METHODS: As part of the On the Move pilot study a project aimed at reducing measurement error in self-reported physical activity measures, we conducted cognitive interviews with 20 men and 20 women, ages 40–65, regarding their responses to 2 physical activity questionnaires currently in use in large, population-based studies. One questionnaire, used in the LACE (Life After Cancer Epidemiology) study, a cohort study of breast cancer survivors, asks about the frequency, duration, and perceived intensity of various activities in several different domains over the past 12 months. The second questionnaire, used in the California Men's health Study (CMHS), a prospective study of etiologic factors for prostate and other cancers, asks about frequency and duration of specific, mostly recreational activities, grouped by intensity (i.e. moderate or vigorous) over the past 3 months. We used verbal probing techniques to allow respondents to describe their thought processes as they completed the questionnaires. All interviews were tape recorded and transcribed. We coded and analyzed the transcripts using modified grounded theory techniques. RESULTS: The cognitive interviews demonstrated that a sizable number of respondents understood “intensity” in terms of emotional or psychological intensity, rather than physical effort. As a result, the perceived intensity with which a participant reported doing a specific activity often bore little relationship to the MET value of that activity. Additionally, participants understood activities that were grouped together in a single category to be definitive, limited lists rather than examples, and they had difficulty dividing an activity, such as walking, into separate domains (i.e. walking for transportation vs. walking for exercise). CONCLUSION: Cognitive interviews reveal significant gaps between researchers' assumptions about what is being measured in physical activity questionnaires and some respondents' answers. Additional research and questionnaire redesign should be undertaken to address these gaps.