In the pharmaceutical industry it is necessary to manage changes to processes or analytical methods to ensure that the quality of drug products is maintained. This often includes an assessment of similarity using data. Scientists may be asked to show that output before and after a change is or will be ‘equivalent’, without clarity on what exactly is required. In the area of analytical methods, the authors have found it useful to promote the differentiation between equivalence and a wider set of comparability approaches. This paper discusses equivalence and comparability, when such approaches should be applied and provides examples of applications to analytical methods. The discussion is then widened to other application areas such as processes including the appropriateness of the approaches and aspects to be considered when designing equivalence studies. Change management, the design of studies and appropriate statistical analysis can be challenging. However, use of the terminology and methodology exemplified here has enabled scientific project teams to focus on appropriate goals and the means to achieve them with great benefits. Copyright © 2011 John Wiley & Sons, Ltd.