Mortality by education level at late-adult ages in Turin: a survival analysis using frailty models with period and cohort approaches

OBJECTIVES Neglecting the presence of unobserved heterogeneity in survival analysis models has been showed to potentially lead to underestimating the effect of the covariates included in the analysis. This study aimed to investigate the role of unobserved heterogeneity of frailty on the estimation of mortality differentials from age 50 on by education level. DESIGN Longitudinal mortality follow-up of the census-based Turin population linked with the city registry office. SETTING Italian North-Western city of Turin, observation window 1971-2007. POPULATION 391 170 men and 456 216 women followed from age 50. PRIMARY OUTCOME MEASURES Mortality rate ratios obtained from survival analysis regression. Models were estimated with and without the component of unobserved heterogeneity of frailty and controlling for mortality improvement over time from both cohort and period perspectives. RESULTS In the majority of cases, the models without frailty estimated a smaller educational gradient than the models with frailty. CONCLUSIONS The results draw the attention of the potential underestimation of the mortality inequalities by socioeconomic levels in survival analysis models when not controlling for unobserved heterogeneity of frailty.