A review of the measures relating to the monitoring of disease progression in Duchenne muscular dystrophy was undertaken as part of the work of the North Star Clinical Network for Paediatric Neuromuscular Disease Management developing a standardized assessment protocol for ambulant children in the UK. This article outlines the process of identifying possible measures. Detailed consideration has been given to key measures of muscle strength and function. As well as the usual assessment of the validity and reliability of the measures, three key characteristics were identified as necessary to the assessment of scales used in health care: (1) the type of scale used; (2) the clinical significance of the attribute being measured; and (3) the mathematical properties of the data provided. Consideration of such aspects in the early stage of a study facilitates the choice of measures, and the analysis and interpretation of data in the longer term.