EBP was first described by David Sackett, a pioneer in introducing EBP in UK healthcare, as follows:

A hierarchy of evidence (Box 1.6) has been developed to provide an indication of the strength of the evidence and therefore, by implication, its usefulness for evidence‐based and evidence‐informed decision making and clinical practice (Draper [9], Ingham‐Broomfield [16]).

Glover et al. ([12]) present for nursing research a hierarchy of evidence as a pyramid (Figure 1.5), with the seventh level or base of the pyramid being ideas, opinions, anecdotes and editorials. Other sources (e.g. Ingham‐Broomfield [16]) have created similar pyramids, and it must be noted that the pyramids vary slightly between authors, organizations and professions.

These hierarchies assume that the most robust evidence is that derived from systematic reviews and meta‐analyses of large‐scale randomized controlled studies (Draper [9], Greenhalgh [13], Ingham‐Broomfield [16]). However, they provide no means of including qualitative research studies (Greenhalgh [13]) or those seeking to answer questions about patients’ experiences or concerns (Del Mar et al. [4]). Draper ([9]) therefore proposes that typologies of evidence are a more appropriate way of defining the quality of evidence. Petticrew and Roberts ([33]) propose the following features to be used in evaluating evidence: effectiveness, service delivery, salience, safety, acceptability, cost‐effectiveness, appropriateness and satisfaction. Glasby et al. ([11]) propose a different approach suggesting three different types of evidence: theoretical, empirical and experiential (Box 1.7).

This typology is reflective of the seminal work of Carper ([1]), who delineated four different forms of knowing encompassed in clinical expertise in nursing. These are:

The issue of determining which evidence is acceptable in practice is evident throughout this manual, where clinical expertise and guidelines inform the actions and rationales of the procedures. Indeed, these other types of evidence are highly important as long as we can still apply scrutiny to their use.

Porter ([34]) describes a wider empirical base upon which nurses make decisions and argues for nurses to take into account and be transparent about other forms of knowledge, such as ethical, personal and aesthetic knowing, echoing Carper ([1]). By doing this, and through acknowledging limitations to these less empirical forms of knowledge, nurses can justify their use of them to some extent. Furthermore, in response to Paley's ([31]) critique of EBP as a failure to holistically assess a situation, nursing needs to guard against cherry picking (i.e. ensuring that EBP is not brandished ubiquitously and indiscriminately) and know when judicious use of, for example, experiential knowledge (as a form of personal knowing) might be more appropriate.

Evidence‐based nursing (EBN) and EBP are differentiated by Scott and McSherry ([39]) in that EBN involves additional elements in its implementation. EBN is regarded as an ongoing process by which evidence is integrated into practice and clinical expertise is critically evaluated against patient involvement and optimal care (Scott and McSherry [39]). For nurses to implement EBN, four key requirements are required (Scott and McSherry [39]):

We contextualize our information and decisions to deliver best practice for patients; that is, the ability to use research evidence and clinical expertise, together with the preferences and circumstances of the patient, is essential to arrive at the best possible decision for a specific patient (Guyatt et al. [14]).

Knowledge can be gained that is both propositional – that is, from research – and non‐propositional – that is, implicit knowledge derived from practice (Rycroft‐Malone et al. [37]). In more tangible, practical terms, evidence can be drawn from a number of different sources, and this pluralistic approach needs to be set in the context of the complex clinical environment in which nurses work in today's NHS (Pearson et al. [32], Rycroft‐Malone et al. [37]). Rycroft‐Malone et al. ([37]) proposed that the evidence that informs clinical nursing practice can be considered as arising from four main sources:

These four sources have all informed the evidence base that is integral to this manual, which acknowledges that ‘in reality practitioners draw on multiple sources of knowledge in the course of their practice and interaction with patients’ (Rycroft‐Malone et al. [37], p.88).