Reliability and validity of self-report and observers' estimates of relative weight

Two studies were done to assess the reliability and validity of observers' ratings and self-reports of relative weight in order to establish procedures for naturalistic studies of obesity. In Study I, observers rated relative weight of college students on a five point rating scale. Self-reports of height and weight of each subject were also obtained. Both the observers' ratings and the self-reports were highly correlated with the measured height and weight data, but self-report data allowed for a more accurate classification of subjects into relative weight categories. Reliability and validity of the observer estimates and the self-reports were calculated using both correlational and percent agreement procedures. Percent agreement provided a more stringent measure of reliability than did the correlational procedures. Study II confirmed the results of Study I for an older, heavier population. Self-report was again superior to observational procedures for weight determination, and percent agreement provided more accurate estimates of reliability and validity than did the correlational techniques.