Patient-reported outcomes are often relevant in studying a variety of diseases and outcomes that cannot be assessed adequately without a patients evaluation and whose key questions require patients input on the impact of a disease or a treatment. To be useful to patients, researchers and decision makers, a patient-reported outcome (PRO) must undergo a validation process to support that it measures what it is intended to measure accurately and reliably. In this workshop, after presentation of some key elements on the development of a PRO measure, the core topics of validity and reliability of a PRO measure will be discussed. Exploratory and confirmatory factor analyses, techniques to understand the underlying structure of a PRO measure, will be described. The topic of mediation modeling will be presented as a way to identify and explain the mechanism that underlies an observed relationship between an independent variable and a dependent variable via the inclusion of a third variable called the mediator variable. Also discussed will be item response theory and, time permitting, longitudinal analysis. Illustrations will be provided mainly through real-life and simulated examples.