In most epidemiological data sets one cannot be certain that all risk factors are measured or observed. This paper studies the risk for mortality associated with diseases and deals with heterogeneity in mortality owing to unobserved covariates. We extracted medical records of 186 hospitalized patients from an urban health facility in Ghana. Patients with at least 2 diagnoses of chronic diseases were considered multimorbid. Using age of patients at death as survival time we executed our analysis with and without incorporating frailty effect to Cox proportional hazards (PH) model. The Cox PH model with Gaussian frailty fitted the data better when compared to the standard Cox PH model and Cox PH model with gamma frailty. On average patients were aged 62.3±15.3 years, with 66.1% being multimorbid. Varying degrees of mortality risks were found for different diseases, with the highest associated with having pulmonary valve disorders (HR 7.99, 95% CI 1.45-44.0). Heterogeneity in mortality resulting from unmeasured factors was insignificant. This study demonstrates that patients share similar risk with respect to unobserved factors, but varying risk when conditioned on observables.
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