Is patients' numeracy related to physical and mental health?

There is compelling evidence showing that health literacy influences health outcomes. However, there is a dearth of research investigating this issue in the vast literature on numeracy-the ability to accurately interpret numerical information about risk, a skill that is only moderately correlated with health literacy. In a cross-sectional study, we investigated whether objective and subjective numeracy is related to objective and subjective health outcomes. Objective (subjective) numeracy is actual (self-reported) numerical competence. Objective outcomes include prevalence of comorbidity and prescribed medications. Subjective outcomes include perceptions of physical and mental health.

A convenience sample of 502 male individuals receiving outpatient care at a Veterans Affairs Medical Center reported their demographics and answered a survey measuring objective and subjective numeracy, trust in physicians, satisfaction with role in medical decision making, perceptions of physical and mental health, and risky habits. We computed patients' body mass index (BMI) and their age-adjusted Charlson index-an extensively studied comorbidity index for predicting mortality in clinical research. We retrieved number of prescribed medications from medical records.

Compared with patients who had high objective numeracy, patients with low objective numeracy showed higher prevalence of comorbidities and took more prescribed medications. Compared with patients who had high subjective numeracy, patients with low subjective numeracy had more negative perceptions of their physical and mental health. These conclusions held after controlling for the effect of demographics, risky habits, BMI, trust in physicians, and satisfaction with role in decision making, suggesting that numeracy has a unique, significant contribution to health outcomes beyond the effect of these factors.

Our research documents for the first time that self-reported numeracy is related to perceptions of health, whereas objective numeracy is related to actual health, laying the groundwork for future research on the effect of numeracy on health outcomes.