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Paper No. 10-08

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M Akacha and JL Hutton

Modelling the rate of change in a longitudinal stiudy with missing data, adjusting for contact attempts

Date: May 2010

Abstract: The Collaborative Ankle Support Trial (CAST) is a longitudinal trial in which interest lies in the rate of improvement, the effectiveness of reminders and potentially informative missingness. A model is proposed for continuous longitudinal data with non-ignorable or informative missingness, taking into account the nature of attempts made to contact initial non-responders. The model combines a non-linear mixed model for the outcome model with a logistic regression model for the reminder process. A sensitivity analysis is used to contrast this model with the traditional selection model, where we adjust for missingness by modelling the missingness process.