How to measure a latent construct: Psychometric principles for the development and validation of measurement instruments.

Measurement instruments are used to collect data about respondents. In social pharmacy, measurement instruments are often used to measure latent constructs, such as attitudes, among healthcare professionals and patients. This paper aims to describe the fundamental aspects of designing and validating instruments, which aim to measure latent constructs. The main focus of this manuscript is to describe the considerations and processes relating to exploratory and confirmatory factor analyses, when used to develop measures of latent psychosocial constructs. However, it also presents a detailed summary of the current evidence and suggestions for item generation and sample selection, as well as, an in-depth description of approaches to content and face validation. Suggestions for further reading are also provided.