Validity of a physical activity questionnaire among African-American Seventh-day Adventists.

INTRODUCTION: Physical activity has been identified as an important predictor of chronic disease risk in numerous studies in which activity levels were measured by questionnaire. Although the validity of physical activity questionnaires has been documented in a number of studies of U.S. adults, few have included a validation analysis among blacks. We have examined the validity and reliability of a physical activity questionnaire that was administered to 165 black Seventh-day Adventists from Southern California. METHODS: Subjects completed a self-administered physical activity questionnaire and then "reference" measures of activity (7-d activity recalls, pedometer readings) and fitness (treadmill test) were completed in subsets of this population. RESULTS: The authors found that 7-d recall activity levels correlated well with the corresponding questionnaire indices among women (total activity, r = 0.65; vigorous, r = 0.85; moderate, r = 0.44; inactivity, r = 0.59; sleep duration, r = 0.52) and men (total activity, r = 0.51; vigorous, r = 0.65; moderate, r = 0.53; inactivity, r = 0.69; sleep duration, r = 0.39). Vigorous activity from 7-d recalls was best measured by gender-specific indices that included only recreational activities among men and emphasized nonrecreational activities among women. Correlations between questionnaire data and the other "reference" measures were lower. Test-retest correlations of questionnaire items over a 6-wk interval were high (r = 0.4-0.9). CONCLUSION: Simple questions can measure activities of different intensity with good validity and reliability among black Adventist men and women.

Urinary 1-methylhistidine is a marker of meat consumption in Black and in White California Seventh-day Adventists.

Meat consumption predicts risk of several chronic diseases. The authors validate the accuracy of meat consumption reported by food frequency questionnaires and the mean of eight 24-hour recalls, using urinary methylhistidine excretion, in 55 Black and 71 White Adventist subjects in Los Angeles and San Diego, California, in 1994-1997. 1-Methylhistidine excretion predicts vegetarian status in Black (p = 0.02) and in White (p = 0.005) subjects. Spearman's correlation coefficients between 1-methylhistidine and estimated meat consumption were usually between 0.4 and 0.6 for both food frequency questionnaires and 24-hour recall data. This is despite the chance collection of dietary recalls and urines from omnivores on meatless days.

Body weight and mortality among adults who never smoked.

In a 12-year prospective study, the authors examined the relation between body mass index (BMI) and mortality among the 20,346 middle-aged (25-54 years) and older (55-84 years) non-Hispanic white cohort members of the Adventist Health Study (California, 1976-1988) who had never smoked cigarettes and had no history of coronary heart disease, cancer, or stroke. In analyses that accounted for putative indicators (weight change relative to 17 years before baseline, death during early follow-up) of pre-existing illness, the authors found a direct positive relation between BMI and all-cause mortality among middle-aged men (minimum risk at BMI (kg/m2) 15-22.3, older men (minimum risk at BMI 13.5-22.3), middle-aged women (minimum risk at BMI 13.9-20.6), and older women who had undergone postmenopausal hormone replacement (minimum risk at BMI 13.4-20.6). Among older women who had not undergone postmenopausal hormone replacement, the authors found a J-shaped relation (minimum risk at BMI 20.7-27.4) in which BMI <20.7 was associated with a twofold increase in mortality risk (hazard ratio (HR) = 2.2, 95% confidence interval (CI) 1.3, 3.5) that was primarily due to cardiovascular and respiratory disease. These findings not only identify adiposity as a risk factor among adults, but also raise the possibility that very lean older women can experience an increased mortality risk that may be due to their lower levels of adipose tissue-derived estrogen.

Validity of dietary recall over 20 years among California Seventh-day Adventists.

Past dietary habits are etiologically important to incident disease. Yet the validity of such measurements from the previous 10-20 years is poorly understood. In this study, the authors correlated food frequency results that were obtained in 1994-1995 but pertained to recalled diet in 1974 with the weighted mean of five random 24-hour dietary recalls obtained by telephone in 1974. The subjects studied were 72 Seventh-day Adventists who lived within 30 miles of Loma Linda, California; had participated in a 1974 validation study; were still alive; and were willing to participate again in 1994. A method was developed to allow correction for random error in the reference data when these data had differentially weighted components. The results showed partially corrected correlation coefficients of greater than 0.30 for coffee, whole milk, eggs, chips, beef, fish, chicken, fruit, and legumes. Higher correlations on average were obtained when the food frequencies were scored simply 1-9, reflecting the nine frequency categories. The 95% confidence intervals for 15 of the 28 correlations excluded zero. Incorporation of portion size information was unhelpful. The authors concluded that in this population, data recalled from 20 years ago should be treated with caution but, for a number of important foods, that the degree of validity achieved approached that obtained when assessing current dietary habits.

Body mass and 26 y risk of mortality among men who never smoked: a re-analysis among men from the Adventist Mortality Study.

OBJECTIVE: To re-analyse the previously reported linear relation between Quetelet's body mass index (BMI) and mortality, among men from the Adventist Mortality Study after accounting for effects due to age at measurement of BMI, smoking history and race. DESIGN: Prospective cohort study. To specifically account for effects due to age at measurement of BMI, smoking history and race, our methodology includes: 1, computing hazard ratios for BMI quintiles from a proportional hazard regression, with 'time on study' as the time variable, and age at baseline as a covariate; 2, conducting separate analyses of middle-aged (age 30-54y) and older (age 55-74y) men; and 3, restriction of the analyses to never-smoking, non-Hispanic white males. SUBJECTS: 5062 men (age: 30-74 y, BMI: 14-44 kg/m2) from the Adventist Mortality Study. MEASUREMENTS: Subjects reported data on anthropometric, demographic, medical, dietary and lifestyle characteristics at baseline and were enrolled in mortality surveillance during a 26y study period (1960-1985). RESULTS: During the early years of follow-up (years 1-8, 9-14), we found some evidence of excess risk among the leanest men that was probably due to the effects of antecedent illness. During the later years of follow-up (years 15-26), effects due to antecedent illness were not apparent and a significant positive, linear relation between BMI and all-cause mortality was consistently found among middle-aged (30-54 y) and older (55-74 y) men. Disease-specific analyses of the later follow-up (years 15-26) revealed that the positive linear trends with all-cause mortality, were primarily due to excess risk of cardiovascular disease and cancer among the heavier men. Among older men, a significant inverse relation between BMI and respiratory disease mortality risk was identified during later follow-up (years 15-26), but this effect attenuated after restriction of the analyses to men with no baseline history of respiratory disease. CONCLUSIONS: The re-analysis confirms the findings of a positive, linear relation between BMI and all-cause mortality, reported in the original study.

Body mass and 26-year risk of mortality from specific diseases among women who never smoked.

We examined the relation between Quetelet's body mass index (BMI) and age-adjusted mortality risk from specific diseases in a 26-year prospective cohort study of 12,576 non-Hispanic white women who had never smoked. To account for effects due to antecedent disease, we focused on women surviving 15-26 years after their report of body weight. High BMI (>27 kg per m2) decreased the risk of fatal respiratory disease (hazard ratios of 0.7 for ages 30-54 years and 0.6 for ages 55-74 years) but increased risk in all other disease categories. Low BMI (<21 kg per m2) increased the risk of fatal respiratory disease (hazard ratios of 2.0 for ages 30-54 years and 1.4 for ages 55-74 years). Among middle-aged women (ages 30-54 years), we found that low BMI also increased the risk of certain fatal cardiovascular diseases (hazard ratios of 1.5 for cerebrovascular death and 2.5 for hypertensive and other cardiovascular deaths), but the increase in the risk of fatal cerebrovascular disease did not remain (hazard ratio of 0.4) after exclusion of subarachnoid and intraparenchymal hemorrhage deaths from the endpoint. Although the inverse relation between BMI and risk of fatal respiratory disease was also evident in the subset who reported body weight 17 years after baseline, further restriction of this subset to stable-weight women reporting no history of respiratory disease resulted in a U-shaped relation. Data from this subset also indicated that weight loss substantially increased the risk of fatal respiratory disease. These findings implicate high and low BMI as risk factors for fatal respiratory disease but suggest that the risk due to high BMI was obscured by weight loss that followed the onset of disease. The overall findings support an association between obesity and a higher risk of fatal disease but also raise the possibility that apparently healthy, never-smoking women can experience a higher long-term risk of fatal cardiovascular and respiratory diseases due to a lower body weight.

Body mass and 26-year risk of mortality among women who never smoked: findings from the Adventist Mortality Study.

The authors have examined the relation between the Quetelet body mass index (BMI) and 26-year risk of all-cause mortality in a population of 12,576 non-Hispanic while, Seventh-day Adventist women (ages 30-74 years) who never smoked. Mortality risk for each BMI quintile (I, < 21.3 kg/m2; II, 21.3-22.9 kg/m2; III, 23.0-24.8 kg/m2; IV, 24.9-27.4 kg/m2; and V, > 27.4 kg/m2) was determined from a proportional hazard regression with adjustment for age and other covariables. In this population, the overall BMI-mortality relation showed dependence on age, duration of follow-up, and baseline indicators of preexisting illness (weight fluctuation, history of major chronic disease, and severe physical complaints). Therefore, the analysis focused on women with no indicators of preexisting illness, and risk estimates were stratified by age at baseline and duration of follow-up. Among middle-aged women (ages 30-54 years), the authors found a weak linear relation during years 1-8 (median attained age, 51 years), a significant linear relation during years 9-14 (median attained age, 57 years), and a significant nonlinear (U-shaped) relation during years 15-26 (median attained age, 68 years). Among older women (ages 55-74 years), they found a significant nonlinear (U-shaped) relation during years 1-8 (median attained age, 71 years) and significant linear relations during years 9-14 (median attained age, 77 years) and years 15-26 (median attained age, 87 years). These findings implicate overweight as a risk factor for fatal disease among women throughout adulthood and raise the possibility that lean, apparently healthy, middle-aged women may experience a higher risk of death during old age due to their lower body weight.

Healthy volunteer effect in a cohort study: temporal resolution in the Adventist Health Study.

The healthy volunteer effect was studied by comparing 6 years of mortality data for 31,124 participants from the Adventist Health Study (AHS) who responded to both a relatively brief census questionnaire (CQ) in 1974 and a detailed life-style questionnaire (LQ) in 1976 (responders), to mortality data for 8,762 individuals who did not respond to the second questionnaire. The rate ratio (RR) comparing LQ nonresponders to responders for all cause mortality decreased from 2.5 (2.2-2.9) in 1977 to 1.4 (1.2-1.7) in 1982 (p for trend = 0.02); for ischemic heart disease mortality from 2.3 (1.8-3.0) to 1.3 (1.0-1.7); and for all sites cancer mortality from 1.8 (1.3-2.5) to 1.5 (1.1-2.0). The death rate decreased markedly among nonresponders and increased slightly among responders during the study. Similar results were seen for age and gender subgroups. Multivariate analysis controlling for confounding variables confirms these results, except that the apparent effect of education is probably due to effect modification by age. The RR decreased to about one after 3 years of follow-up in young subjects but remained elevated (> 2) in older subjects. Available sociodemographic information reveals that a higher proportion of responders are married, have college education, are SDA church members, and use medical services less than nonresponders during the previous year. Because the risk remains elevated at the end of the study in some but not all subgroups, it seems reasonable that the elevated risk in nonresponders may be due in part to a less healthy life style and in part to exclusion of individuals who did not feel well during enrollment. The results suggest that for internal comparisons no bias is likely to occur; but descriptive statistics for certain subgroup comparisons, and external comparisons, may be biased by the healthy volunteer effect.

Effect of risk factor values on lifetime risk of and age at first coronary event. The Adventist Health Study.

The effect of traditional coronary heart disease risk factors on lifetime risk, age at onset, and survival free of coronary disease has not been extensively studied. The authors have used the cohort data from 27,321 California Seventh-day Adventists who had no known heart disease in 1976 to investigate these questions. Multiple decrement life tables incorporating non-parametric estimates of conditional probabilities for both coronary disease and all other competing endpoints were used to estimate these survival outcomes. Variance estimators are provided in an appendix. Persons characterized by being either past smokers, diabetic, hypertensive, physically, non-vegetarian, or infrequent consumers of nuts often showed substantial differences in these survival outcomes. Statistically significant results include earlier age at onset of coronary disease at between 4 and 10 years, reduced life expectancy free of the disease between 5 and 9 years, and increased lifetime risk between 8% and 16%, when comparing groups with and without adverse values for different risk factors. The presence of adverse levels of two risk factors predicted even greater differences in these endpoints. These important effects are easily understood by the layman or non-epidemiologist professional, which is often not true of a relative risk. This should increase the effectiveness of such results when promoting behavioral change.

The relationship between cardiorespiratory fitness, physical activity, and dietary quality.

This study evaluated the relationship between cardiorespiratory fitness, physical activity, and dietary quality in a group of 20- to 40-year-old women (n = 34) who varied widely in levels of physical activity. Nutrient intakes were determined using 10 repeated 24-hr diet records, randomly assigned, over a 10-week period. Physical activity was determined on the same randomly assigned days using the Caltrac Personal Activity Computer. Cardiorespiratory fitness was assessed by two maximal graded treadmill tests with continuous metabolic monitoring at both the beginning and end of the 10-week period. Neither physical activity nor cardiorespiratory fitness was significantly correlated with nutrient density (nutrient/1,000 kcal). Intake of energy (kcal/kg body weight) was higher for the more physically active and fit women, leading to a significant increase in most nutrients consumed per kilogram of body weight.

Effects of walnuts on serum lipid levels and blood pressure in normal men.

BACKGROUND: In a recent six-year follow-up study, we found that frequent consumption of nuts was associated with a reduced risk of ischemic heart disease. To explore possible explanations for this finding, we studied the effects of nut consumption on serum lipids and blood pressure. METHODS: We randomly placed 18 healthy men on two mixed natural diets, each diet to be followed for four weeks. Both diets conformed to the National Cholesterol Education Program Step 1 diet and contained identical foods and macronutrients, except that 20 percent of the calories of one diet (the walnut diet) were derived from walnuts (offset by lesser amounts of fatty foods, meat, and visible fat [oils, margarine, and butter]). RESULTS: With the reference diet, the mean (+/- SD) serum values for total, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol were, respectively, 182 +/- 23, 112 +/- 16, and 47 +/- 11 mg per deciliter (4.71 +/- 0.59, 2.90 +/- 0.41, and 1.22 +/- 0.28 mmol per liter). With the walnut diet, the mean total cholesterol level was 22.4 mg per deciliter (0.58 mmol per liter) lower than the mean level with the reference diet (95 percent confidence interval, 28 to 17 mg per deciliter [0.72 to 0.44 mmol per liter]); the LDL and HDL cholesterol levels were, respectively, 18.2 mg per deciliter (0.47 mmol per liter) (P < 0.001) and 2.3 mg per deciliter (0.06 mmol per liter) (P = 0.01) lower. These lower values represented reductions of 12.4, 16.3, and 4.9 percent in the levels of total, LDL, and HDL cholesterol, respectively. The ratio of LDL cholesterol to HDL cholesterol was also lowered (P < 0.001) by the walnut diet. Mean blood-pressure values did not change during either dietary period. CONCLUSIONS: Incorporating moderate quantities of walnuts into the recommended cholesterol-lowering diet while maintaining the intake of total dietary fat and calories decreases serum levels of total cholesterol and favorably modifies the lipoprotein profile in normal men. The long-term effects of walnut consumption and the extension of this finding to other population groups deserve further study.

Root-form implants placed in subantral grafted sites.

Life-table analysis of survival data of implants placed in subantral grafts reveals a high rate of survival, particularly in comparison with implants placed in non-grafted subantral sites. However, sample size (158 grafted, 140 non-grafted, in a total of 120 patients) and follow-up time remain insufficient to reach a definite conclusion. Results also appear improved over other reports in which the sinus was penetrated by the implants, possibly because the procedure has become more standard over the years.

Coffee consumption and cause-specific mortality. Association with age at death and compression of mortality.

The relationship between reported coffee consumption and specific causes of death was examined in 9484 males enrolled in the Adventist Mortality Study in 1960 and followed through 1985. Coffee consumption was divided into three levels: less than 1 cup per day, 1-2 cups per day, and greater than or equal to 3 cups per day. Approximately one third of the subjects did not drink coffee. Cause-specific mortality rates were compared using survival analysis including Cox's proportional hazard model, and controlling for potential confounders such as body mass index, heart disease and hypertension at baseline, race, physical activity, marital status, educational level, smoking history, and dietary pattern. Inclusion of interaction terms between coffee consumption and attained age as time-dependent covariates allowed the hazard ratio to vary with age. Univariate analyses showed a statistically significant association (p less than 0.05) for coffee consumption and mortality for most endpoints. Multivariate analyses showed a small but statistically significant association between coffee consumption and mortality from ischemic heart disease, other cardiovascular diseases, all cardiovascular diseases, and all causes of death. For the major causes of death, the hazard ratios decreased from about 2.5 at 30 years of age to 1.0 around 95 years of age. These results indicate that abstinence from coffee leads to compression of mortality rather than an increase in lifespan.

Body mass index and patterns of mortality among Seventh-day Adventist men.

This study examines the relationship between body mass index (BMI) and 26-year mortality among 8828 nonsmoking, nondrinking Seventh-day Adventist men, including 439 who were very lean (BMI less than 20 kg/m2). The adjusted relative risk comparing the lowest BMI quintile (less than 22.3) to the highest (greater than 27.5 kg/m2) was 0.70 (95 percent CI 0.63-0.78) for all cause mortality, 0.60 (95 percent CI 0.43-0.85) for cerebrovascular mortality, and 0.80 (95 percent CI 0.61-1.04) for cancer mortality. Very lean men did not show increased mortality. To assess whether the protective effect associated with low BMI is modified by increasing age, the product term between BMI and attained age (age at the end of follow-up or at death) was included as a time-dependent covariate. For ischemic heart disease mortality, age-specific estimates of the relative risk for the lowest quintile relative to the highest ranged from 0.32 (95 percent CI, 0.19-0.52) at age 50 to 0.71 (95 percent CI, 0.56-0.89) at age 90. Interaction was also seen for the next lowest quintile (22.4-24.2). There was a significant trend of increasing mortality with increasing BMI for all endpoints studied. For cancer and cerebrovascular mortality the P-values for trend were 0.0001 and 0.001 respectively. For the other endpoints the P-values were less than 0.0001. Thus, there was no evidence for a J-shaped relationship between BMI and mortality in males. While the protective effect associated with the lowest BMI quintile decreased with increasing age for ischemic heart disease mortality, it remained greater than one at all ages. The relatively large number of subjects who were lean by choice, rather than as a result of preclinical disease or smoking, may explain these findings.

Self-report of physical activity and patterns of mortality in Seventh-Day Adventist men.

The Adventist Mortality Study provides 26-year follow-up through 1985 for 9484 males who completed a lifestyle questionnaire in 1960. The relationship of self-reported physical activity and all cause and disease-specific mortality was examined by survival analysis and with the Cox proportional hazards model, controlling for demographic and lifestyle characteristics. Moderate activity was associated with a protective effect on cardiovascular and all cause mortality in both analyses. In the Cox model, age-specific estimates of relative risk (RR) were obtained for several endpoints due to a significant interaction between level of physical activity and attained age (age at death or end of follow-up). This model permits calculation of the age at which the RR = 1.0, or the age at crossover of risk. For moderate activity, this age was 95.6 years (95% confidence intervals, 81.7-109.4 years) for all cause mortality and 91.5 years (95% confidence intervals, 79.0-104.0 years) for cardiovascular mortality. While the protective effect on mortality associated with moderate activity decreased with increasing age, it remained significant to the verge of the present life span.

Attained height of lacto-ovo vegetarian children and adolescents.

The relationship between diet and attained height was studied in children and adolescents in Southern California. Diet pattern was determined from an extensive food frequency questionnaire in 1765 Caucasian children of 7-18 years, attending state schools (452 m and 443 f) and Seventh-day Adventist schools (427 m and 443 f). The major difference in diet pattern between state and Adventist school children was in meat consumption. The Adventist children were split evenly between three categories of frequency in meat consumption (less than 1/week, 1/week-less than 1/d, and greater than or equal to 1/d), while 92 percent of state school children consumed meat daily. Vegetarians (those consuming meat less than 1/week) differed significantly in the consumption of other major food groups, such as fruit and vegetables. All school and diet subgroups were at or above the 50th percentile of the National Center for Health Statistics. Age-adjusted regression analysis showed that on average Adventist vegetarian children were taller than their meat-consuming classmates (2.5 and 2.0 cm for boys and girls, respectively). These results did not change materially when adjusting for other food groups. Nor did adjustment for parental height and socioeconomic factors in a sub-sample of 518 children. The results indicate that vegetarian children and adolescents on a balanced diet grow at least as tall as children who consume meat.

Anthropometric parameters of schoolchildren with different life-styles.

Height and weight data obtained from a 2-year longitudinal survey were analyzed for 2272 children aged 6 through 18 years who were attending public schools or Seventh-Day Adventist (SDA) schools in southern California. The SDAs do not use alcohol or tobacco, and many adhere to a lacto-ovovegetarian diet. For both sexes, in each school group, the mean height and weight were at or above national reference values. Age-adjusted regression analysis showed that SDA school-boys were 1.6 cm taller than public schoolboys. There were no significant differences in height for girls. After controlling for height, boys and girls in the SDA schools were found to be leaner than their public school peers, ie, 1.27 and 1.16 kg, respectively. These results suggest that a health-oriented life-style in childhood and adolescence, such as the one followed by SDAs, is compatible with adequate growth and associated with a lower weight for height.

Determinants of eight-year diet recall ability.

This study investigated how well people can recall their food habits of years ago and identified factors that predict recall ability. We examined the self-reported dietary intakes of 623 people, about one-third of whom were vegetarians. Subjects included cancer cases and controls who were selected as a representative sample of the Adventist Health Study population. We compared the initial (1976) dietary data with data recalled retrospectively in 1984. The initial and retrospective assessments made use of the same food frequency questionnaire for the same 35 food items. Recall ability was measured in two ways: exact recall and recall error. Persons with a stable diet had by far the best recall. Vegetarian status and level of education also were determinants of exact recall, whereas diet stability and education were the most significant determinants of recall error. These results indicate that some individuals, particularly those with a stable diet, those with a vegetarian diet, and those with more education, are able to recall their past dietary practices with reasonable reliability.

Reliability of eight-year diet recall in cancer cases and controls.

We addressed three questions concerning diet recall in a population of 181 incident cancer cases diagnosed between 1976 and 1984 in the Adventist Health Study, and 225 controls randomly selected from the same population after removing cancer cases: (1) Are recalls of past dietary habits reliable? (2) Does recall ability differ between cancer cases and controls? and (3) Are current or retrospectively recalled reports the best estimator of past dietary practices? Three sets of dietary data were compared using a 35-item nonquantitative food frequency questionnaire: initial reports in 1976, recalled reports obtained retrospectively in 1984, and current reports for 1984. Recall ability was evaluated for individual foods and for all foods combined by comparing recall error scores summing the absolute differences between initial and recalled frequencies. Means and medians for all three food groups were similar for cases and controls. The Spearman rank-order correlations between pairs of reports (initial/recalled, initial/current, and recalled/current) averaged 0.48, 0.41, and 0.62, respectively. A crude difference of 2.0 between cases and controls (p less than 0.05) in the recall error score indicated that cases on the average recalled two foods one frequency category closer to the initial estimate compared with controls. The case-control difference decreased to a nonsignificant 0.4 (p = 0.07) in multivariate analysis that conditioned on dietary changes. On the average, recalled reports estimated initial reports one frequency category closer than did current reports for three foods (p less than 0.001), primarily because of changes in dietary habits.

Husband-wife diet concordance and changes in dietary practices by surviving spouses of cancer cases.

Diet concordance and changes in dietary practices by surviving spouses of cancer cases were investigated by studying 69 husband-wife pairs during an eight-year period spanning the death from cancer of one spouse. The data base consisted of reports for each cancer case from the Adventist Health Study (AHS) where a surviving spouse was available. Two questions were addressed. 1. Do husbands and wives eat similar diets? 2. Did survivors change their diet practices during the eight-year period? Three sets of dietary data were compared with the AHS food frequency questionnaire: reports made in 1976 by cases; reports made in 1976 by their spouses (initial); and the spouses' reports in 1984 (current). Diet concordance and dietary changes for 35 key food groups were evaluated both for individual foods and across foods by computing recall scores. The results were analyzed with univariate and multivariate methods. Comparison of means and Spearman rank-order correlations revealed good initial concordance between the spouses, which was not significantly related to age, sex, or education. However, eight years later subsequent to the deaths of the cases, the agreement was poor because the surviving spouses had changed their diets. The changes in dietary practices were significantly related to education and body mass index in univariate analysis but not in analysis of covariance. These results indicate that retrospective recall by spouses for the cases rather than the spouses' own current reports should be used as an estimate for the deceased cases. Repeated recalls are necessary to increase reliability.