Chapter 1: What types of evidence are needed for evidence-informed decision-making?

Evidence is defined as factual knowledge gained through observation or experimentation in support of a conclusion [19]^,[20]. Evidence can be broadly grouped into tacit and scientific evidence. Tacit (or colloquial) knowledge is mostly informal, and often includes opinions, values and habits of policy-makers, clinicians, patients or citizens expressed in different forms in formal deliberative dialogues, on websites, in policy documents, reports, and other formats [19]^,[21]^,[22]^,[23]. Scientific or research evidence, on the other hand, refers to knowledge that is explicit, systematic and replicable, and can be judged by its methodological standards [19]. Scientific evidence is produced through more formal, rigorous research processes, including primary studies (primary research), synthesis of existing evidence (secondary research), and evidence products such as guidelines or evidence briefs for policy (EBPs) (tertiary research) [1]. (See Chapter 2 for an explanation of these types of evidence.)

The relationship between tacit and scientific evidence is complementary rather than competitive [19]^,[24]. In EIDM, tacit evidence is often used to support, complement or question the appropriateness of scientific evidence, and extends the evidence ecosystem [21]^,[25]. One example of tacit evidence is expert opinion, which combines facts, interpretation of those facts, and conclusions [26]. As academic, commercial, financial and ideological factors can affect expert interpretation, factual evidence supporting an expert opinion should be distinguished and appraised separately when making official recommendations [26]. This helps to avoid conflicts of interest that mislead judgements on a policy issue or new research endeavour [21].

As an additional distinction, scientific evidence can also be assessed for its relevance at global, regional or local level. Global evidence assembles the best available findings on a specific thematic or health issue from around the world [20], and can be synthesized in the form of a systematic review or operationalized in a tertiary research product such as a guideline. As all evidence is context-specific, global evidence is, however, not always easily transferable to a specific local context, and its applicability beyond the original contexts or settings needs to be assessed and judged carefully [27]. Additional local evidence, including observations in a specific setting, administrative data or primary studies, needs to be consulted to take into account modifying factors such as local prevalence of a disease, local perceptions and values, or cost and available resources [20]^,[28].

Overview of different types of evidence used in EIDM

• Scientific (codified) evidence is produced through formal, rigorous research processes of defined methodological standards, making it explicit, systematic and replicable [19].

• Tacit (colloquial) evidence often includes opinions, expertise, lessons learned, organizational tradition of policy-makers, clinicians, patients or citizens and helps to contextualize and interpret scientific evidence further [19]^,[21]^,[22]^,[23].

• Global evidence assembles the best available findings on a specific thematic or health issue from around the world, e.g. through a systematic review or an established, evidence-informed guideline [20].

• Local evidence takes into account modifying factors in specific settings, e.g. through a primary study or programme monitoring data [20]^,[28].

The distinctions of evidence discussed here are not mutually exclusive and overlap at several points. Different issues or policy problems call for different types of evidence, and different opinions may exist as to what constitutes the best available evidence for a particular question [20]. EIDM and evidence-informed policy-making emphasize the use of relevant and applicable evidence to improve policies and programmes, and ensure that evidence is assessed in a systematic and transparent manner unaffected by conflicts of interest [20].

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