What role does socio-economic position play in the link between functional limitations and self-rated health: France vs. USA?

BACKGROUND Our objective was to analyse the influence of education on the link between functional limitation (FL) and self-rated health (SRH) in two countries, France and the USA. METHODS The data of the North American NHANES study (n = 9254) and the French National Health Survey (n = 25 559) were used. FL was measured by the ADL and IADL scales. We constructed a logistic regression model with SRH as the outcome and included variables for education, FL and the interaction between education and FL. All results were adjusted for age. RESULTS Poor SRH was more frequently reported in France than in the USA (24.1% vs. 18.4% for men, 29.0% vs. 19.7% for women). The most highly educated persons in the USA had similar FL (25.4% for men, 32.9% for women) to the least educated French persons (22.8% for men, 31.8% for women). In the USA, FL was associated more strongly with poor SRH in the most educated men than in the least educated. In France, the same interaction was observed although the link was weaker than in the USA. FL was more strongly associated with poor SRH in the most educated women than in the least educated in both countries. CONCLUSION Functional limitation had a greater impact on the most highly educated persons in both France and the USA. Using SRH as a measure of health for evaluating social inequalities could lead to underestimation of the true magnitude of functional health inequalities existing within and between countries.