Prevalence: What Is the Nature and Scale of the Problem?

Asking the question, “how many clients need our services?” may be one of the simplest questions to ask, but it can be one of the hardest questions to answer. Knowing the number of clients who may need your service is a crucial first step in planning your policy, your service response, and your practitioner and client needs. Within this chapter we explore this challenge. We introduce the concept of prevalence, and we provide a range of approaches to estimating it. These approaches range from those that require less resources and expertise such as from simple case finding and counting to those that may require more resources, such as surveys and benchmark multiplier methods. We then introduce more advanced statistical methods. We illustrate how these methods can be used ensuring good research practice in terms of client identification and finally we demonstrate how to apply the methods in two case studies one involving people who inject drugs and one involving children of parents who use drugs.