A new approach to evaluate quality adjusted life years using proxy utility function - An application to HIV/ AIDS data

Estimation of Quality Adjusted Life Years (QALYs) is pivotal towards economic evaluation and cost-effectiveness analysis of medical interventions. Most of the methods developed till date for calculating QALYs are based on multi- state structures where fixed utility values are assigned to each disease state and total QALYs are calculated on the basis of total lengths of stay in each state. In this article, we have presented a new proxy approach to define utility as a function of risk factors, which can be used to calculate QALY without defining discrete disease states. Retrospective survival data of HIV/ AIDS patients undergoing treatment at the Antiretroviral Therapy (ART) center of Ram Manohar Lohia hospital in New Delhi has been used to demonstrate implementation of the proposed methodology. Joint modelling, with a mixed effect longitudinal sub-model for CD4 count and a Cox proportional hazard survival sub-model with time dependent covariates, has been used to estimate risks associated with different factors and covariates. Using the proxy utilities, QALYs have been calculated for each individual for their lifetime time horizon, defined as the time since their registration in the ART till death or till their age reach average life expectancy of HIV/ AIDS patients in India. QALY results are consistent with findings of conventional cost-effectiveness studies on ART for HIV/ AIDS patients in India.