Optimism, pessimism and bias in self-reported body weight among older adults

Body mass index (BMI) and obesity (BMI ≥ 30) are often derived from self-reported weight and height; psychological dispositions may bias how participants report these physical characteristics. The present research used a large national sample of US adults to examine the correspondence between reported and measured body weight and height and to test whether optimists and pessimists misreport their weight/height in ways that are consistent with their worldviews.

Participants in the Health and Retirement Study (N = 11,207) reported their weight and height and completed a measure of dispositional optimism and pessimism; trained interviewers measured participants' weight and height.

There was a high correlation between measured and reported weight (r = 0.98) and height (r = 0.92). Consistent with their positive and negative worldviews, respectively, optimists under-reported and pessimists over-reported their weight. There was not a consistent association with misreported height. Optimism and pessimism were also associated with actual BMI and risk of obesity, but the protective/risk effects were amplified when using reported weight to derive BMI.

These findings suggested that reported body weight tends to be accurate, but that biases associated with psychological dispositions may inflate the relation between the disposition and obesity. Such biases may extend to associations with other self-reported factors thought to be related to optimism and pessimism.