Past exam of the mathematics course of the University of Cambridge / 2019 / iii / Paper 207 / 3 / 3 / 4 / a

The monthly nurse assessments are auxiliary longitudinal outcomes observed even after clinic dropout. Investigators can include their histories, treatment, and earlier QoL in a multiple imputation model for missing 12-month QoL, or in a joint longitudinal model. Because the assessments predict disability and QoL, conditioning on them reduces residual outcome variance and makes each imputed value more informative, improving precision of the treatment-effect estimate. A prespecified covariate-adjusted or augmented inverse-probability estimator could use the same information.