Accommodating informative dropout and death: a joint modelling approach for longitudinal and semicompeting risks data

Both dropout and death can truncate observation of a longitudinal outcome. Since extrapolation beyond death is often not appropriate, it is desirable to obtain the longitudinal outcome profile of a population given being alive. We propose a new likelihood-based approach to accommodating informative dropout and death by jointly modelling the longitudinal outcome and semi-competing event times of dropout and death, with an important feature that the conditional longitudinal profile of being alive can be conveniently obtained in a closed form. We use proposed methods to estimate different longitudinal profiles of CD4 count for patients from the HIV Epidemiology Research Study.