Working within the EBLIP process, librarians need to assemble evidence from a variety of sources that are most appropriate to the problem or question at hand. Assembling evidence is key to the whole concept of EBP, and determining the sources of evidence that one will draw upon when making practice-based decisions is paramount. We must use professional judgement to determine the best and most appropriate sources of evidence, depending upon what we want to know. Evidence may come from external sources, locally gathered data or our own professional knowledge. This chapter will start with an overview of the concept of evidence and how it relates to librarianship, explore different types of evidence and look more specifically at sources of evidence within librarianship and how to find the needed evidence. The goal of this chapter is to expand your thinking about what evidence is and to help you determine some of the sources that you can draw upon. Being evidence based means that we consider many forms of evidence in conjunction with one another to form a well informed and considered professional opinion.

The concept of evidence

To begin considering what types of evidence we should seek and then use as part of decision making within librarianship, we first need to ask ‘what is evidence’ within our field. This is no small question, but one that underlines the whole evidence-based approach.

The Oxford Dictionary (2010) states that evidence is ‘the available body of facts or information indicating whether a belief or proposition is true or valid’. Scholars agree that evidence is that which serves as a form of proof (Hornikx, 2005; Reynolds and Reynolds, 2002; Twinning, 2003; Upshur, Van Den Kerkhof and Goel, 2001). Schrum (2011) notes that evidence has three major properties – relevance, credibility and inferential force or weight (p. 19). This means that, to be considered as evidence, pieces of information must be relevant to the question at hand, must be considered credible or trustworthy and must show strength in comparison to other pieces of information that are being considered. We will consider how to assess the credibility and weight of evidence in more detail later, in Chapter 5.