Evaluate existing evidence

Laatst bijgewerkt op: 19-03-2026

Once the potential effects of an intervention have been identified with the effect map, the next step is to examine to what extent these effects have already been explored in existing research. This helps to avoid unnecessary duplication of research efforts. It is inefficient to invest time, resources, and effort in studying effects for which sufficient evidence is already available. The exploration of existing evidence may lead to insights that were not anticipated at an earlier stage. If this is the case, revise the effect map to reflect these new insights.

Literature research

The search for existing evidence on effects is conducted through a literature review. A literature review is a systematic approach to identifying, collecting, analysing, and synthesising existing research findings, and drawing conclusions based on the evidence found.

There are different approaches to conducting a literature review, ranging from a full systematic review to a more practice-oriented rapid review. Each approach has its own methodological guidance, for example on the development of search strategies to identify relevant literature, summarising findings from the literature, and the appraisal of the quality of the literature. Different methods also draw on different types of literature.

Scientific and grey literature

For researching existing evidence, it is relevant to use, in addition to literature published in scientific journals, literature that is disseminated through other channels. Examples include publications from healthcare organisations, knowledge institutes, policy documents, experiential accounts, news articles, factsheets, blogs, theses, and doctoral dissertations. This is referred to as grey literature and is not disseminated through scientific journals. Grey literature can be published more quickly than scientific literature and may therefore contain the most up-to-date insights.

Collecting information

Once you have found the relevant literature for the effect to be investigated, you need to consider what information you would like to extract. This involves collecting all information on the selected effect of the innovation in a specific population. A PICOT (Patient, Intervention, Comparison, Outcome, Time) may be used to guide this process.

However, there is more information that is useful to record. For example, the sample size or tips for implementing an intervention or other effects that were not initially in mind but were found relevant while reading the literature.

Record all the information in a structured data extraction form, to ensure a clear overview of the information from the different publications.

Assessing quality

Finally, it is important to assess the quality of the articles. For this, Vilans, in collaboration with other research partners, has developed a framework: the AACODS-NL. The AACODS-NL comprises of 23 questions divided across six themes: authority, accuracy, coverage, objectivity, date, and significance. These questions are answered for each piece of literature, which ultimately results in a score per theme.

The scores are used in the evaluation of existing evidence. This provides an overview of the quality of the information found. This can help to reach agreement on when the evidence is considered sufficient.

The AACODS-NL (in Dutch) can be downloaded via the web version of the Value Palette Framework.