Estimating a treatment effect from multidimensional longitudinal data

Multidimensional longitudinal data result when researchers measure an outco me through time that is quantified by many different response variables. Th ese response variables are often defined on different numerical scales. The objective of this paper is to present a method to summarize and estimate a n overall treatment effect from this type of longitudinal data. A regressio n model is proposed that assumes the treatment effect can be parameterized as an acceleration or deceleration of the time scale of each response varia ble's trajectory. Generalised estimating equations are used to estimate the model parameters. Cognitive and functional ability data from Alzheimer's d isease patients and quality of life data from an AIDS clinical trial are us ed to illustrate the model.