Table describes the characteristics of the study population. The mean (standard error [SE]) age was 43.14 (0.38) years, about 51.25% was female, and slightly more than three-fourths were non-Hispanic Whites with similar proportions reported completion of tertiary-level education or less, and annual incomes of less than $50,000. About half of the adult female population (44.45 percent) and almost two-thirds (61.74 percent) of the male population reported having smoked 100 cigarettes in the past.
General characteristics of males and females in the Third National Health and Nutrition Survey, 1988–1994.
Almost 30 percent of males reported having tried to lose weight in the past 12 months with about one-fourth attempting to lose weight at the time of the interview. The proportions for females were about 50 and 40 percent, respectively. About half of the men interviewed (49.10 percent) said they wanted to weigh less than their current weight, while this figure for females was 69.99 percent. About half of the females interviewed felt that they were overweight, compared to only 42.61 percent of males. A quarter of all women and 19 percent of all men interviewed reported that they were less active than people of the same age. The distribution of levels of health perception by the participants and assessment by a medical examiner were similar for males and females. The average number of months since the last visit to a health professional was 15 months for males and 8 months for females.
The mean BMI was 26 kg/m2 for both men and women. The average measured weight was 81.57 kg for males and 68.87 kg for females. Average self-reported weight was 82.06 kg and 67.24 kg for males and females, respectively.
Using ordered logistic regression, the crude odds ratios of the association of the degree of discrepancy in weight and selected characteristics are given in table . Compared to the 30 to 39 age group, younger males and those greater than 80 years of age were more likely to overestimate their weight (p ≤ 0.01). In contrast, females of at least 60 years of age were more likely to overestimate their weight (p ≤ 0.01). In both sexes, increasing age was associated with a higher probability of discrepancy.
Odds ratios of crude ordered logistic regression analysis examining the probability of a discrepancy between self-reported and measured weight by selected characteristics. Third National Health and Nutrition Examination Survey, 1988–1994.
Non-Hispanic black and Mexican-American males were 66 percent (95% CI: 41% to 95%) and 16 percent (95% CI: 1% to 32%) more likely, respectively, to overestimate their weight compared to their non-Hispanic white counterparts. For females, non-Hispanic blacks were no more likely to report discrepancies in weight compared to non-Hispanic whites. However, Mexican-American women and women of other races were 17 percent (95% CI: 1% to 35%) and 29 percent (95% CI: 2% to 62%) more likely to overestimate their weight.
The attainment of a primary education in males was associated with an increase of 1.364 (95% CI: 1.132 to 1.643) in the odds of overestimating measured weight by self report compared to those attaining a tertiary education. Secondary education was associated with an increase of a similar magnitude. Results were similar for females.
The association between annual income and the degree of discrepancy in weight is statistically evident only in the upper income brackets. Compared to those earning $20,000 to $29,000 a year, males earning more than $40,000 a year are more likely to underestimate their weight (p ≤ 0.05). For females, this association is evident at a much lower income bracket ($30,000, p ≤ 0.05).
Smoking more than 100 cigarettes in the past was associated with an increase of 27 percent (95% CI: 11% to 46%) in the chances of overestimating weight. This association was seen in males only.
Participants who, in the past year, attempted to lose weight were more likely to underestimate their weight during the interview (males: OR = 0.488; 95% CI: 0.420 to 0.567; females: OR = 0.605; 95% CI: 0.532 to 0.689). Similar associations were found among those who were currently attempting to lose weight.
Discrepancy in self-reported weight was found to reflect the desires and perceptions of the participants. The desire to weigh more and the perception of being underweight was each associated with a two-fold increase in the likelihood of overestimating weight during the interview. A similar two-fold increase in the chance of reporting a lower weight was seen when participants reported a desire to weigh less or when they perceived themselves to be overweight.
Self-reported level of activity and the number of months since the last visit to a health professional were associated with a discrepancy in self-reported weight only in women. Compared to women who reported comparable levels of activity with people of the same age, women who considered themselves more active were 1.183 times (95% CI: 1.060 to 1.319) more likely to overestimate their weight. An increase in one year since the last visit to a health professional was associated with a 3 percent increase (95% CI: 0.3% to 6%) in the likelihood on underestimating one's weight.
The participants' perception of their health status was associated with a disagreement between self-reported and measured weight only in the two worst levels. Compared to a rating of "good," males reporting their health as being "fair" and "poor" were 1.303 and 1.536 times more likely, respectively, to overestimate their weights (p ≤ 0.01). For females, this association was statistically evident only in those reporting "fair" health (OR = 1.336; 95% CI: 1.104 to 1.616).
Similarly, a medical professional's assessment of health was associated with a discrepancy in self-reported weight only in the extremes of the scale. For males, this was apparent only in those whose health was assessed as being "poor;" in females, an association was found only in those with a rating of "excellent." Compared to those with a rating of "good," males with a "poor" rating were 1.818 times (95% CI: 1.102 to 3.000) more likely to overestimate their weights. Females with a rating of "excellent" were 1.197 times (95% CI: 1.015 to 1.413) more likely to overestimate their weights.
BMI was associated with decreasing trends in the odds ratios in both sexes (p for trend < 0.0001). Using a BMI of 18.5 to 24.9 as the reference group, males and females with a BMI of less than 18.5 were 2.659 (95% CI: 1.522 to 4.646) and 3.642 (95% CI: 2.580 to 5.143) times more likely to overestimate their weights, respectively. Underestimation of weight was associated with higher BMI categories. For females, overweight, obesity I, II, and III statuses were associated with 47%, 66%, 76% and 87% increases in the likelihood of underestimating their weights, respectively. These values were 55%, 74%, 89%, and 94% for males, respectively.
The application of a multiple ordered logistic regression model to the predictors produced the estimates of association shown in table . Separate models are given for males and females. For both sexes, important predictors of the degree of discrepancy in self-reported weight include age, race-ethnicity, highest educational attainment, and measured BMI. For males alone, additional predictors were cigarette smoking and the desire to change weight. For females, marital status, annual income, level of activity, and the length of time since the participant's last visit to a health professional were important.
Multiple ordered logistic regression of the predictors of the discrepancy between self-reported and measured body weight by sex in the Third National Health and Nutrition Examination Survey, 1988–1994.
Adjustment of other covariates reversed the direction of effect of age in males and females. Compared to those aged 30 to 39, males and females aged less than 20 years were found to be 20 (95% CI: 6% to 47%) and 44 percent (95% CI: 23% to 60%) more likely, respectively, to underestimate their weights. No other statistically significant associations were found for other age group in males. Females older than 60 years, however, were more likely to overestimate their weights with the oldest age group being 3.3 times more likely than those in the reference group.
The adjusted effect of race-ethnicity in males was similar to the crude estimates. For females, however, non-Hispanic blacks, a group previously found to be no more likely to misreport their weights during the analysis of crude effects, were shown to have 1.369 times (95% CI: 1.145 to 1.636) the odds of overestimation compared to their non-Hispanic white counterparts. The estimates for Mexican-Americans and women of other groups were only slightly increased after adjustment.
The estimated effects of BMI and highest educational attainment after adjustment were similar to estimates of their crude effects, as were the adjusted effects of cigarette smoking and desire to change weight in males, and annual income and the length of time since the participant's last visit to a health professional in females.
Utilizing these figures, estimates of the proportions of males and females in the NHANES III by the degree of discrepancy between self-reported and measured weight stratified by age are given in table and represented graphically in figure . Overall, more than 35 percent of males overestimate their weight by 2 kilograms or more; in females, this proportion is only about 14 percent. About a 35 percent of all females underestimate their weight, compared to about 25 percent for males. Although the proportion of people correctly reporting their weight to within 1 kilogram was approximately constant throughout the age range, a greater proportion of the elderly was shown to overestimate, and of the young to underestimate, their weights.
Crude and adjusted proportions with discrepancies* between self-reported and measured weight, by extent of discrepancy, sex, and age in the Third National Health and Nutrition Examination Survey, 1988–1994.
Proportions with discrepancies between self-reported and measured weight, by extent of discrepancy, sex, and age in the Third National Health and Nutrition Examination Survey, 1988–1994.