Participant Adherence

The terms compliance and adherence are often used interchangeably. In 1979, Haynes et al., defined compliance as “the extent to which a person’s behavior (in terms of taking medications, following diets or executing lifestyle changes) coincides with medical or health advice” [1]. More recently, an international consensus statement crafted by the World Health Organization and the International Society of Pharmacoeconomics and Outcomes Research defined medication adherence as “the extent to which a patient acts in accordance with the prescribed interval and dose of a dosing regime” [2]. Patient adherence is also recently reviewed in additional articles [3–5]. The term adherence implies active participant involvement in the decision to take a medication, use a device or engage in a behavior change, and is the term used in this book. In this chapter, we primarily refer to drug adherence but the concepts apply generally. In a drug trial, adherence typically refers to ingestion of predetermined amount of drug such as 80% of the protocol dose. This dose will depend on the nature and half-life of the drug being evaluated. Persistence is a related term that refers to remaining on a medical treatment for a specified period of time, regardless of the proportion of the doses taken. Distinguishing adherence vs. persistence is important since the metrics are different as well as the implications for trial interpretation [6, 7].