Recall of Physical Activity in the Distant Past: The 32-Year Follow-up of the Prospective Population Study of Women in Göteborg, Sweden

Lauren Lissner1,2 , Nancy Potischman3, Richard Troiano3 and Calle Bengtsson1

1 Institute of Community Medicine (Primary Health Care), Sahlgrenska Academy at Göteborg University, Göteborg, Sweden.
2 Nordic School of Public Health, Göteborg, Sweden.
3 Applied Research Program, National Cancer Institute, Bethesda, MD.

Received for publication February 6, 2003; accepted for publication August 19, 2003.


    ABSTRACT
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
It has been of interest to researchers in chronic disease epidemiology to determine whether elderly subjects can accurately recall their physical activity patterns in the distant past. As part of a 32-year follow-up of the Prospective Population Study of Women in Göteborg, Sweden, 433 participants currently aged 70–92 years recalled their leisure-time physical activity at the original examination in 1968, when they had been 38–60 years of age. Using a four-point scale, subjects were originally asked to describe leisure-time activity during the previous 12 months. Identical questions were asked in 2000 describing levels in 1968 and current levels. Subjects were more likely to overestimate their previous activity level than to underestimate it: 43.9% of women classified themselves consistently at both examinations; 48.7% overestimated and 7.4% underestimated their previous activity levels. Using current activity as a proxy for recalled levels did not improve the moderate agreement with activity as originally reported in 1968. The average magnitude of the recall bias (recalled minus original values) amounted to one half of a unit on the four-point scale and was not significantly associated with age or body mass index. In summary, systematic errors were observed in remote physical activity recalls by elderly women, who generally remembered being more active 32 years earlier than they had originally reported. Physical activity recall questionnaires for the distant past should be used with caution, particularly in older populations.

bias (epidemiology); exercise; mental recall; prospective studies; women

Abbreviations: Abbreviation: CI, confidence interval.


    INTRODUCTION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Given the increasing evidence that physical activity is an important protective risk factor for many chronic diseases, it has been of methodological interest to determine whether elderly subjects can accurately recall their physical activity patterns in the distant past. In a recent issue of the Journal, Falkner et al. (1) described participant characteristics and quality of recall of physical activity. Using data from 137 surviving members of a cohort followed since the early 1960s, the authors concluded that individual respondent characteristics had little association with recall of past physical activity, but that current activity may influence recall and is therefore an important factor to consider. Recall of weekday activity levels was consistently underestimated, while "free-day" (weekend) activity patterns tended to be overreported in most groups. Reporting biases of this type are likely to vary across the populations studied, and we would like to report briefly on a similar study conducted in a cohort of Swedish women.


    MATERIALS AND METHODS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Study design and sample
In 1968, a population-based sample of 1,622 women aged 38, 44, 50, 54, and 60 years was identified from the population registries of Göteborg, Sweden, and invited to participate in a health examination. Over 90 percent of these potential subjects then attended the baseline examination of the Prospective Population Study of Women in Göteborg. The original sample has subsequently been reexamined on several occasions, most recently in 2000. Over the years, significant attrition has occurred, primarily because of death but also because of relocation and refusal. The overall participation rate for the 32-year follow-up was 71 percent among the subjects who were still alive, and the characteristics of surviving women who did not participate in the most recent examination have been documented recently (2). Specifically, although dropouts did differ from participants with respect to some baseline health indicators, no significant differences in 1968 physical activity levels were observed. As part of the 32-year follow-up, 433 of the original participants, now aged 70–92 (mean, 75.8) years, were asked to recall their leisure-time physical activity patterns at the baseline examination in 1968.

Subjects had originally been asked during a physician-conducted interview in 1968 to describe their leisure-time physical activity during the previous 12 months, using a four-point scale that has been validated and described previously (3, 4). Leisure activity group I consisted of women who were "almost completely inactive" with examples of reading, watching television, and movies; group II reported "some physical activity at least 4 hours per week," with examples such as biking and walking; group III engaged in "regular physical activity" such as jogging, aerobic exercise, and tennis; and group IV included "regular heavy physical training and competition" with examples such as competitive sports. Identical questions were asked in 2000, to describe both current activity levels and recollections of activity levels 32 years previously. This study has been approved by the Ethics Committee of Göteborg University.

Statistical methods
Recall bias was calculated as the difference between original and recalled values, and a general linear model was used to test whether age and body mass index were associated with recall bias. Age at baseline was treated as a continuous variable, while body mass index was used both in its continuous form and as above or below the group median. The weighted kappa statistic was used to describe pair-wise agreement among the three activity variables of interest here: originally reported in 1968; recalled in 2000; and current estimate in 2000. Because the highest activity level reported in 1968 was not represented in this sample, the weighted kappa statistics have excluded 10 subjects reporting extreme values in their recall or current activity levels in 2000, resulting in an n x n (3 x 3) format required for the kappa coefficient.


    RESULTS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
These data allowed evaluation of how consistently subjects recalled their past activity levels. As shown in the top portion of table 1, the women were far more likely to overestimate their previous activity level than to underreport it. Comparison of the original activity estimates with distant recalls of these levels revealed that 48.7 percent overestimated their previous activity levels, 43.9 percent of women classified themselves identically at the two examinations, and 7.4 percent underestimated their activity levels 32 years earlier. As shown in figure 1, the overall agreement was only moderate (weighted kappa = 0.11, 95 percent confidence interval (CI): 0.04, 0.19).


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TABLE 1. Cross-classification of response frequencies for original activity levels, recalled levels, and current levels in 2000,* Göteborg, Sweden
 


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FIGURE 1. Weighted kappa coefficients (with 95% confidence limits) between original leisure-time activity levels (estimated contemporaneously in 1968), recalled physical activity levels estimated in 2000 to reflect levels in 1968, and current activity levels estimated in 2000 by 423 women from Göteborg, Sweden, all reflecting agreement in activity categories I–III.

 
The remaining sections of table 1 illustrate agreement between recalled and current levels, both assessed in 2000, and finally between current 2000 levels and original 1968 values. Although 88 women (20.32 percent) who were currently active recalled that they were active in 1968, in fact only 24 (5.54 percent) actually reported being active in 1968. The agreement between original and current activity (weighted kappa = 0.10, 95 percent CI: 0.05, 0.16) was almost identical to that observed between original and recalled activity levels. In contrast, a stronger agreement was observed between current and recalled levels (weighted kappa = 0.29, 95 percent CI: 0.22, 0.36).

The mean values for each physical activity variable are given in the single-dagger footnote of table 1. Based on these data, an indicator of recall bias was quantified as the difference between recalled and originally reported levels for each subject. The average reporting error (calculated as activity levels recalled in 2000 minus originally reported levels) was 0.47 units (standard deviation = 0.72; t = 13.5, p < 0.0001). This indicates that the systematic overreporting bias was on the order of one-half point, on a scale of one through four. A further multivariate regression analysis was conducted in which the recall bias was modeled as a function of age and body mass index. Neither of these subject characteristics was significantly associated with the amount of recall bias. All age groups and both body mass index groups (above or below 22.7 kg/m2 at baseline) overreported to a similar extent, by approximately one-half activity point on average. For instance, in the five age groups, the body mass index-adjusted estimates of bias were 0.42 (in the youngest), 0.53, 0.47, 0.44, and 0.49 (in the oldest), indicating a similar magnitude of overreporting with age. Likewise, the average age-adjusted bias estimates were quite similar across body mass index categories: 0.46 and 0.48 in the leaner and heavier women, respectively. However, regression analysis stratified on the median body mass index yielded some additional insight into the possible role of body mass index in relation to recall bias. Specifically, the age-adjusted association between original and recalled activitities in the below-median group was statistically stronger (p < 0.0002) than that observed in the heavier women (p < 0.02), and the weighted kappa values indicated corresponding differences by weight status (coefficients of 0.16 and 0.05, respectively). Thus, both heavier and leaner groups displayed similar general tendencies to overreport, but the strength of associations in the respective groups may indicate better validity among leaner women.


    DISCUSSION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
In conclusion, there is a systematic lack of agreement between the leisure-time activity levels reported in the distant past and recalls of these previous levels by the same women at much older ages. Women generally recalled being more active 32 years earlier than they had originally reported. The overreporting appeared to be largely independent of age and weight status at the original examination, although there was some indication of more random error in the recalls given by relatively heavier women. Alternatively, using current activity levels as a proxy for earlier levels does not provide an improved estimate of activity in the distant past. The highest degree of agreement was observed between current and recalled levels, which may reflect the fact that the questions on current and recalled activity at the most recent examination were asked consecutively. Similar effects of current habits on the recall of remote habits have been observed for nutrient intake in other study populations completing dietary history interviews (5).

A possible limitation of the data presented here is the fact that no subject in the follow-up subsample had originally reported being in the most highly active group. We initially speculated that this category might not have been used in 1968; however, closer inspection of the data from the entire original sample indicated that several subjects had in fact been in this category in 1968, although none of those participated in the 32-year follow-up. Thus, activity level IV was an acceptable answer in 1968 but, as confirmed by the original examining physician (C. B.), participation in competitive sports was uncommon among middle-aged women at the end of the 1960s. Nonetheless, it must be emphasized that the analysis was limited by the necessity of reducing the physical activity variable to a three-point scale. We cannot exclude the possibility that the bias and lack of agreement observed here reflect weak design features of the questionnaire, and that better agreement might have been achieved with a more detailed scale.

These data may be compared with those from another study of similar duration (1) that, interestingly, observed an opposite (underreporting) bias with respect to recall of occupational activity reported in the distant past, although this did not reach statistical significance in females. Reports of free-day (leisure-time) activities were recalled at a nonsignificantly higher level than the original reports in women. Other studies involving the validity of recalled activity levels have been based on much shorter recall intervals (68). Comparisons among studies are complicated by the various methods of assessment and analysis, as well as by the age of the participants in this study.

From a practical point of view, it is of interest to know whether current activity estimates are superior indicators of originally reported activity levels, compared with recalled values. Our results suggested that remotely recalled activity estimates perform no better than current estimates, when using original values as the standard. In conclusion, collection of remote recall data on physical activity, particularly in elderly populations, should be undertaken with caution.


    ACKNOWLEDGMENTS
 
This study was funded by grants from the Swedish Research Council (345-2001-6652, 27X-04578) and the Bank of Sweden Tercentary Foundation.

The authors thank Dr. Gordon Willis for his suggestions and assistance with the analyses.


    NOTES
 
Correspondence to Dr. Lauren Lissner, Department of Primary Health Care, Sahlgrenska Academy at Göteborg University, Box 454, 405 30 Göteborg, Sweden (e-mail: Lauren.Lissner{at}medfak.gu.se). Back


    REFERENCES
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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