Over-Adjustment Bias by Controlling for Overall Health

DEAR EDITOR, Should we control for overall health if we want to know whether higher social capital is associated with more physical activity? Is it reasonable to adjust for overall health if we want to explore the effect of a series of health behaviors on primary health‐care use? What if we want to understand how attitude about aging determines the trajectory of functional health over time? What if we want to test if overall health mediates the association between pain and depression? I say No to the first three questions, and i say Yes to the last two questions, but why? Ueshima et al. conducted a study among 2260 individuals in Japan to test if social capital has any protective effect on physical activity. They, however, controlled for self‐rated health in their final model. Could the effect of social capital on physical activity be through an enhancement in overall health? If yes, we do not need to control for overall health. To me, it seems quite reasonable to assume that social capital first improves health perception and then those people who feel healthier would engage or report more physical activity. Another example is a paper published in 2012 in Family Practice. The study tested the effect of various behaviors such as smoking, alcohol abuse, excessive alcohol intake, use of soft drugs, and insufficient physical exercise on primary health‐care utilization. This study showed that 1Center for Research on Ethnicity, Culture and Health, School of Public Health, University of Michigan, Ann Arbor, United States, 2Department of Health Behavior and Health Education, School of Public Health, University of Michigan, Ann Arbor, United States Correspondence to: Dr. Shervin Assari, Department of Health Behavior and Health Education, School of Public Health, University of Michigan, Ann Arbor, United State E‐mail: [email protected]