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Which evidence to use when?

Published onApr 25, 2024
Which evidence to use when?

EIDM relies on using the best available evidence [142],[143], which, in turn, depends on both the question that needs answering, the best study design for the question, the quality of the evidence, and the context for the decision (see Chapter 1 and Table 1.1 for further guidance on choosing between the different types of research evidence). For example, questions asking “what works” are best answered by systematic reviews of experimental designs. For questions related to understanding “how an intervention works or fails to work”, a mix of qualitative and quantitative designs are needed.

At the same time, the context of the question at hand will influence which type of evidence is needed. For example, when determining local priorities or the acceptability of a policy option in the specific context, local evidence is needed. To determine if an intervention works across settings, suiTable evidence includes national, regional or global research – here, systematic reviews of intervention studies will prove most useful.

Table 3.1 shows the sources of evidence often used for different questions linked to both the policy/action cycle and the evidence funnel. It lists sources of existing research evidence and mostly includes primary and secondary research. However, in the process of applying the steps of the policy/action cycle, evidence will also be created – including primary, secondary and tertiary research.

Source: adapted from WHO Regional Office for the Eastern Mediterranean 2019 [69].

a. Household and facility surveys are a source of descriptive data about a population or health facilities. Household surveys can be used to collect a variety of information, including sociodemographic, health behaviours and health outcomes. Facility surveys can collect information such as inputs, processes of care, outputs like service utilization, and sometimes health outcomes at health facility level.

b. Surveillance studies or systems require the systematic and continuous collection, analysis, and interpretation of data, such as information about cases of notifiable diseases, and of the adverse effects of pharmaceuticals.

c. Routine health information includes data from vital registration systems, such as births and deaths, causes of death, hospital admission records, and outpatient visit records.

d. Burden of disease studies use existing data and research to assess mortality and disability from major diseases, injuries, and risk factors using the metric of the disability-adjusted life year (DALY). This metric allows comparisons between different diseases, injuries, and risk factors.

e. This step requires the creation of evidence (primary research). There is unlikely to be pre-existing evidence that will help, although the analysis of national surveys and routine health information may prove useful. Also, previous research can help to inform the methods and indicators used.

How do I deal with insufficient research evidence?

At times, policy, programme or practice decisions need to be made even when there is insufficient research evidence available on possible impacts. For EIDM, the best available research evidence should always be used, and a thorough search for available research conducted. In the absence of a systematic review about the impact of a policy option, a rapid review of the evidence [144],[145],[146] should be considered. If a rapid review is conducted, a full systematic review should be considered at a later date.

In the absence of a systematic review or rapid review of effectiveness, primary studies can be consulted. If none are available, it may be appropriate to draw on other types of evidence, such as indirect evidenced1 and, as a last resort, tacit (colloquial) knowledge (see Chapter 1) [19],[21]. Participatory processes that involve stakeholders, such as those used for the development of recommendations within guidelines, can help to ensure due process [147],[148],[149], but the uncertainty in the decision should nonetheless be acknowledged [19],[26]. When decisions are made based on insufficient research evidence, a well-designed evaluation (of process, outcomes and impacts) is necessary, for example in the form of a pilot study prior to fully rolling out the policy or programme [144],[150].

Often, decision-makers will face individuals or groups bringing forward various types of evidence and other information to address a specific problem. Fig. 3.1 provides an overview of the evidence types commonly considered in policy decision-making, which may be presented to decision-makers in ways that place more visibility on some types than on others (e.g., data analytics, modeling and evaluation), even when other types may be more appropriate for answering the most pressing questions at a given point in the policy-making process (i.e., a systematic review of effectiveness studies to provide information about which options are best) (see also column 2 in exhibit 4.8, and exhibit 4.13 [67]). The best evidence – in the form of evidence synthesis combined with high quality local studies – should be distinguished from other evidence types and additional information such as tacit knowledge including expert opinions or panels, jurisdictional scans (exhibit 4.8 [67]), or outputs from citizens’ panels. Nonetheless, these additional forms of evidence often offer value and can be used complementarily (see columns 3 and 4 in exhibit 4.8 [67], and Fig. 3.1).

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