Measuring clinically relevant change in apathy symptoms in ADMET and ADMET 2.

Objectives: Among participants with Alzheimer's disease (AD) we estimated the minimal clinically important difference (MCID) in apathy symptom severity on three scales.

Design: Retrospective anchor- and distribution-based analyses of change in apathy symptom scores.

Setting: Apathy in Dementia Methylphenidate Trial (ADMET) and ADMET 2 randomized controlled trials conducted at three and ten clinics specialized in dementia care in United States and Canada, respectively.