Design of pilot studies to inform the construction of composite outcome？measures

Composite scales have recently been proposed as outcome measures for clinical trials. For example, the Preclinical Alzheimer's Cognitive Composite (PACC) is the sum of z-score normed component measures assessing episodic memory, timed executive function, and global cognition. Alternative methods of calculating composite total scores using the weighted sum of the component measures that maximize the signal-to-noise ratio of the resulting composite score have been proposed. Optimal weights can be estimated from pilot data, but it is an open question how large a pilot trial is required to calculate reliably optimal weights