Rounding as an indicator of bias in reported body weight in health surveys.

Due to the higher costs and selection bias of directly measuring weight, the majority of body weight data are based on survey responses. However, these statements are subject to systematic biases of social desirability; therefore, it is important to evaluate the magnitude of bias through indirect indicators such as rounding of weights. Data from seven rounds of the Spanish National Health Survey from 1995 to 2017 were included in the study, with 113,284 subjects. A general rounding index of weights terminating in 0 and 5, and a partial rounding index that estimated the bias direction, were used to estimate the bias distribution in the self-reporting of body weight. All body weights were systematically rounded, although more strongly in the lower weights and even more so in the higher weights. Lower weights were rounded up, and the higher weights rounded down. Regarding gender, men had higher rounding indices than women. The subjects generally reported a weight closer to the socially desirable weight. Rounding allows estimating the historical evolution of this bias in health and nutrition surveys, having more accurate information by population segments and designing public policies against obesity aimed at the more affected social segments.

[Nutrition-related knowledge scarcely leads to any eating habit changes. The case of working-class mothers in Andalusia, Spain]. / El conocimiento nutricional apenas altera las practicas de alimentación: el caso de las madres de clases populares en Andalucía.

Many prevention-oriented public health policies consist of informative campaigns. These campaigns are based on the idea that information is the key to changing the practices on the part of the population thinking that, once provided with the necessary information, the subjects would change their living habits to more healthy ones. However, many studies have refuted this belief: There is a major gap between what is known about nutrition and actual everyday eating habits. An analysis is provided of this overall dynamic in the case of working-class mothers based on the results of qualitative research done in Andalusia on eating habits and discourses. Here also, we find a major gap between what is known about nutrition and actual everyday eating habits. In this article, an analysis is made of the reasons for this discrepancy as well as of the dynamics leading to continual distortions and reinterpretations of the messages given out by the health authorities. Based on these analyses, recommendations are proposed with a view to public health policy: Instead of general informative campaigns, more localized actions or actions which would have a bearing on the material living conditions would be more effective.