Review question / Objective: The first aim is to descriptively synthesize evidence about response shift results including prevalence and, where possible, distributions of response shift effect sizes, for different subcategories of response shift methods, populations, study designs, and patient-reported outcome measures (PROMs). The second aim is to identify response shift methods, population characteristics, design characteristics and PROMs that explain variability in: (a) standardized mean differences (for then-test and latent variable methods) and (b) prevalence of response shifts. Condition being studied: The systematic review included all studies on response shifts in PROMs, irrespective of the condition being studied. The type of health condition that each individual study focused on (if applicable), was extracted as a study-level variable.