The sample was almost evenly divided between African Americans and whites; men constituted approximately 35% in each racial group. Forty-three percent had only a grade school education, an additional 28% had not completed high school. Fifty-nine percent reported an annual income of less than $7,500. All were 71 years of age or older, one third was at least 80 years of age.
There was close agreement between self-reported and measured height, weight, and BMI (ICC = 0.85, 0.97, and 0.91, respectively, for the entire sample; for BMI normal, overweight, and obese, height ICC was 0.88, 0.84, and 0.78, respectively, and 0.92, 0.95, 0.92 for weight). When the difference between self-reported and measured status was calculated as a percentage of measured status, height was incorrectly estimated to a greater extent than weight (height: 1.8% overestimate for both men and women; weight: 0.8% overestimate for men, 0.1% for women).
Analysis of variance of the total group indicated that neither education nor income reached statistical significance, but that there were statistically significant differences by race, age group, and the interaction of sex and age group for height; and by race and age group for weight. Accordingly, we report information by race; race and sex; and race, sex, and age category (). includes three panels. The first gives raw data on the total sample, the second on African Americans, and the third on whites. Both African Americans and whites (panel 1) overestimated their height (whites on average by 3.35 cm, and African Americans by 2.77 cm, p = .0015). On the other hand, while whites underestimated their weight, on average by 0.19 kg, African Americans overestimated their weight, on average by 0.74 kg (p < .0001). Overall, however, both African Americans and whites underestimated BMI.
Descriptive Characteristics of the Sample by Measured (and self-reported minus measured) Height (m), Weight (kg) BMI (kg/m2)
As age increased, so did average overestimation of height and weight. The differences across age groups in these overestimations were significant (height, age 71–74: 2.41 cm; 75–79: 3.30 cm; 80–84: 3.38 cm; 85 years and older: 3.81 cm; p < .0001; weight: 0.02, 0.05, 0.38, and 1.45 kg, respectively, p = .0029). The only statistically significant interaction was between sex and age group for height (p = .0291). Among women, height overestimation increased consistently with age, among men it did not.
Further examination explored responses within each racial group. Among African Americans (panel 2), both men and women overestimated their height (each by an average of 2.79 cm), and weight (on average 1.2 kg for men and 0.46 kg for women). Except among the oldest age group, women tended to increasingly overestimate their height with increase in age, but among men, overestimation was consistent at approximately 2.54 cm until age 85, when it doubled. Both African American men and women overestimated their weight. Weight overestimation was not closely linked to age for African American men, but for African American women underestimation of weight by those less than 80 years of age changed to overestimation of weight, on average by 0.98 kg at age 80–84, and by 2.35 kg at age 85 and older.
In the white sample (panel 3), as in African Americans, height was overestimated by both sexes. Among the white men, there was no consistent effect of age on overestimation of height. Women showed an increase in overestimation of height with age. Estimations of weight were inconsistent with age for both the white men and the white women, but overestimation was greatest in the oldest age group. With a single exception (the oldest African American women), BMI was always underestimated because of overestimation of height.
shows, for African Americans and whites, the extent to which BMI category based on self-report agreed with measured BMI category (values in bold indicate percent agreement). We did not subset further by sex because of the small numbers in the extreme BMI categories.
Self-report-based BMI Cross-tabulated by Measurement-Based BMI Separately for African Americans and Whites (N [row %])
For African Americans, category-specific agreement ranged from 66% to 78%. Underestimation of measured category (the values to the right of the diagonal [in bold]) ranged from 31% (for the underweight) to about 20% each for the normal, overweight, and obese I categories. Overestimation (values to the left of the diagonal), occurred for 22% for those in the obese II+ category, but were less for those in the normal, overweight, and obese I categories (3%, 9%, and 12%, respectively). For whites, complete agreement as to category ranged from 63% to 96% (the latter for obese II+); underestimation was comparable with that of African Americans, except for greater self-reported underweight. Overestimation, however, was lower, ranging from 1% to 10%. Weighted kappa (agreement beyond chance) was 0.76 for African Americans and 0.75 for whites. Looking specifically at identification of overweight or greater (BMI ≥25), for African Americans sensitivity and specificity was 0.89 and 0.90, respectively, while for whites it was 0.66 and 0.96. Identification of the obese (BMI ≥30), had sensitivity and specificity of 0.81 and 0.97 for African Americans, and 0.57 and 0.99 for whites.
The differences between measured and self-reported weight ranged from an underestimate of 19.5 kg to an overestimate of 20.4 kg, with approximately 90% of the values lying within 5 kg of the measured weight (Supplementary Table 1
). For both African Americans and whites, overreporting of weight by the underweight changed linearly to underreporting by the obese, with the differences from measured weight statistically significant in adjacent BMI categories.