What is evidence?

Evidence is most commonly thought of as proof supporting a claim or belief. For public health interventions, evidence typically refers to the effectiveness of an intervention in achieving an outcome that will create lasting changes in the health of the population. This evidence is usually published in scientific literature such as in professional journals, books, or government reports.

The Guide to Community Preventive Services (Community Guide) provides recommendations based on evidence gathered through rigorous and systematic reviews of published studies. The review includes the study designs used, the number of studies conducted, the consistency of the findings, the effect sizes found and expert opinion. The rigorous approach of the Community Guide in defining evidence summarizes what is known about the effectiveness, economic efficiency and feasibility of interventions to promote community health and prevent disease. Recommendations made by the Task Force on Community Preventive Services are considered the gold standard for evidence-base interventions because of the criteria used for evaluation.

Another similar review, the Evidence-Based Practice Program, takes into consideration studies that utilize a variety of study designs in the review of evidence for cancer control interventions. By incorporating a broader definition of evidence in determining criteria for inclusion, other types of interventions may be recommended. Examples may include interventions that demonstrate positive health or behavioral outcomes, but have less rigorous evaluation designs, those on a federal agency “best practices list” or those with an insufficient period of time between intervention and evaluation to demonstrate a sizeable impact.

Despite the relatively new application of evidence-based public health interventions, the focus has already expanded from scientific credibility alone to the inclusion of more practical considerations. Often, the interventions published in the scientific literature are conducted in academic or research settings supported by skilled evaluators, space, equipment, technology, funding and other resources. In community-based settings, personnel or material resources, financial costs, training and other implementation concerns may pose challenges to conducting or evaluating an intervention.

As a result, many public health professionals have found other ways to describe or demonstrate the effectiveness of their interventions. The terms best practice, promising practice, exemplary practice and model intervention are also used interchangeably with evidence in public health settings. These recommendations may be based on evidence that the intervention has been developed, implemented and evaluated according to behavioral science theories or models that have been successful in creating changes in health-related outcomes in other communities.

Because definitions of these terms that are used interchangeably often have great variation and less specificity, their application to assessing the effectiveness of interventions has been limited. The various definitions provided for “evidence” suggest the emergence of an evidence-based continuum, ranging from methodological criteria based on a traditional scientific paradigm (e.g., a randomized, controlled trial) to descriptive criteria documented through process-oriented reports (e.g., best practices). The following table provides a summary of criteria to describe an evidence continuum.

Evidence Continuum

Criteria

Rigorous scientific evidence

Participatory research-based evidence

Participatory practice-based evidence

Quality of evidence

Randomized, controlled study design

Other study designs (e.g., case study)

No study design

Volume of evidence

Replicated in multiple studies

One or more quality studies

Not necessarily replicated

Time from intervention to outcome

Short interval (e.g., less than 4 years)

May have a longer interval

May have a longer interval

Decision-maker

Individual (scientist or evaluator)

Group (coalition, program staff)

Group (coalition, program staff)

Intervention focus

Individual or interpersonal relations (clinical or experimental)

Populations (behaviors, interpersonal relations, organizations, environments, or policies)

Populations (behaviors, interpersonal relations, organizations, environments, or policies)

Funding required

Grant funded (expensive)

Mix of grants, foundations, or government funds

Mix of grants, foundations, or government funds

Training of practitioners

Certification required

No certification required

No certification required

Resources required

Often more space, equipment, technology, materials

Often less space, equipment, technology, materials

Often less space, equipment, technology, materials

Sustained impact

Unknown - intervention and evaluation typically occur in 4 years or less

Unknown – intervention may endure in the absence of evaluation

Unknown – intervention may endure in the absence of evaluation


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