1 Department of Social and Preventive Medicine, School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY.
2 Department of Cancer Prevention, Epidemiology, and Biostatistics, Roswell Park Cancer Institute, Buffalo, NY.
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ABSTRACT |
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epidemiologic methods; exercise; recall
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INTRODUCTION |
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MATERIALS AND METHODS |
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The present sample consists of survivors of the Buffalo Health Study living in western New York who were reinterviewed between 1992 and 1996. Participants were primarily White (93.4 percent) with 48.2 percent male, 51.8 percent female, and 73.7 percent married. The mean age at the re-interview (recall) was 58.4 (standard deviation, 6.3) years, and the mean level of education was 12.5 (standard deviation, 2.4) years. Our previous report (9) describes the questionnaire used to obtain the original and recalled reports of physical activity. Current physical activity reports were obtained using the Stanford Five-City Project questionnaire (15
).
To compare reports, we computed indices of physical activity utilizing guidelines from the compendium of physical activities by Ainsworth et al. (16). The energy expenditure for each activity reported was calculated as the product of the activity-specific metabolic equivalent, duration in hours, and body weight in kilograms. Indices were expressed as the mean metabolic equivalents per kilogram per hour computed as the sum of all reported activities divided by the total number of hours reported and body weight. Indices were further classified into weekday indices and free-day indices.
The quality of recall was defined as the difference between original and recalled reports. Values near zero indicated the best recall, positive values indicated overestimation, and negative values indicated underestimation. Good recallers were participants with the smallest differences between the original and recalled reports (±1 standard deviation of the mean difference of the entire group from zero). Participants with differences greater than one standard deviation above zero were overestimators; those with differences less than one standard deviation below zero were underestimators.
In both the original and the recall interviews, demographic information, height, and weight were obtained by self-report. The age at the recall interview was examined as a continuous variable and in three groups: less than 52 years, 5262 years, and more than 62 years (originally less than 20, 2030, and more than 30 years, respectively). Education was examined as continuous as well as categorical variables: less than 12 years, 12 years, and more than 12 years. Marital status was divided into married and not married (single, widowed, divorced, separated). The body mass index was calculated as weight (kg)/height (m)2. Blood pressure at the original interview is reported as the mean of three measurements. The reported blood pressure and pulse at the recall interviews are the mean of three measurements in the seated position after 5 minutes of rest.
The original, recalled, and current reports were compared with t tests and analysis of variance with post hoc Tukey testing. To assess the association of subject characteristics with quality of recall, analysis of variance was used. In addition, analysis of variance and the chi-square statistic were used to compare good recallers with over- and underestimators. Adjusting for possible confounders did not affect our results; therefore, those data are not shown. SPSS for Windows was used for all analyses (17).
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RESULTS |
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For weekday activity, although not statistically significant, good recallers tended to be younger and better educated than others (table 2). Furthermore, good recallers had lower levels of current weekday physical activity compared with over- and underestimators (males, p < 0.05).
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DISCUSSION |
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Although we found some differences by gender, the evidence did not strongly support better recall by one sex over the other. Three previous studies (1012
) also found no difference in recall by gender. The study by Cumming and Klineberg (13
) found decreased reproducibility with older age, cognitive impairment, and male gender. This was a reproducibility study, however, and all participants were older than 65 years.
We also found some differences by age for recall of past free-day activity with the youngest females underestimating and all others overestimating. Age did not influence the recall of past weekday activity, however. One citation (13) reported reduced reproducibility in older participants, but all were aged more than 65 years. Hence, the evidence does not support the association of age with quality of recall. Although good recallers tended to have more education than over- and underestimators, all differences were nonsignificant statistically. Marital status in 1960 appeared to be associated with the recall of past free-day activity, but this difference seems to be related to a difference in age between those married and those unmarried. In addition, marital status was not related to differences in recall of weekday activity or with marital status at the recall interview. Thus, it is unlikely that marital status was associated with the quality of recall of past physical activity.
We found that good recallers had lower levels and overestimators tended to have the highest levels of current physical activity. This finding is in agreement with the literature (11) and provides additional information that current activity may influence recall of past activity. We suggest that, when follow-up of established cohorts is planned, a section on current physical activity be included. A section on recall of past physical activity should also be added, and analyses similar to what has been reported here should be completed to further clarify the association of current activity with the quality of recall of past activity.
We examined data in tables 2 and 3 for outliers and found that those with the greatest differences between original and recalled reports did not have extremes of age, education, current physical activity, blood pressure, or pulse nor were they more likely to be males or females, Whites, or non-Whites. In contrast to another study (18) where obese women misreported the level of physical activity to a greater degree than did lean women, we found limited variation in body weight or body mass index among good recallers and over- and underestimators, and we found no extreme values in any of the three groups.
The lack of greater differences between good recallers and over- and underestimators could be related to the definitions of these groups and the small number of over- and underestimators. The definitions are conservative, however, and good recallers comprised about 70 percent of the study sample, leaving the most extreme cases of over- and underestimation as the ones most likely to be different. Other definitions of good recallers were assessed with similar results (data not shown). Therefore, in this study and with the characteristics examined, we have confidence that, with the exception of current physical activity, participant characteristics have little association with the quality of recall of past physical activity.
The small study sample and the percentage of the original cohort reinterviewed (6 percent) are limitations of this study; however, sample sizes greater than 150200 have not been shown to produce substantial improvements in precision and reliability (19). Therefore, although the results may not be representative of the general population, this study is comparable with other reliability studies.
The availability of the records from more than 30 years ago provided a unique opportunity to add to the limited information available on the recall of physical activity in the distant past. Previous studies utilized records from 110 years prior, and few influences on recall were found (1013
). Our results provide additional evidence that respondent characteristics have little association with the quality of recall of past physical activity. On the other hand, current physical activity was associated with recall and, as such, current physical activity should be considered in studies that investigate past physical activity and chronic disease risk.
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ACKNOWLEDGMENTS |
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The authors acknowledge the founding work of Dr. Warren Winkelstein, Jr., who developed the original Buffalo Health Study. His foresight and thoughtfulness are to be commended. The authors further thank him for making the 1960 data available to them and for answering their many questions.
Additional thanks are extended to Dr. Joyce Vana for her advice and assistance in the preparation of this manuscript and to Dr. John Weiner for his guidance with statistical issues and questions.
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NOTES |
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REFERENCES |
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