Search strategy

The search strategy was refined into two concepts following the application of PICO. Concept 1 is ‘Sedentary behaviour or inactivity’ and Concept 2 is ‘Intellectual Disability’. Each of the two concepts will be searched using MESH terms and keywords and then combined using OR. Then the total results of each concept will be combined using AND (See Figure 1). This search will be repeated for each of the four databases. The resulting article list will be the complete combined database search results. This list will be screened for inclusion.

Search string. An example of the search string used for the Medline database is shown in Table 1.

Screening process. All identified articles from each database that is searched, as well as all grey literature sources, will be combined and duplicates removed. Endnote software will be used to store all the identified articles. The articles will be stored in folders which are named after the search process used. Using the inclusion criteria as detailed above, all articles will initially be screened by title and then by abstract. The remaining full text articles will be retrieved and read thoroughly. Those that do not meet the inclusion criteria will be omitted. The remaining articles will then be quality assessed using two separate assessors with a third person as an adjudicator should any discrepancies arise.

Quality assessment and risk of bias. The remaining articles will be assessed using two validated quality assessment tools from the National Institute of Health ( National Institute Health, 2020), the first for observational cohort and cross-sectional studies and the second for randomised controlled trials (RCTs). The tools used are available as extended data ( Lynch, 2020).

These tools are used to critically assess the internal validity of each article and identify any issues or sources of potential bias. According to Cochrane, effectively evaluating the quality of a study is done by looking at its design, methodology, results, analysis and reporting, and how they relate to the original research question ( Higgins et al., 2011).

There are different types of study quality assessment tools for the different study types. For Controlled Intervention Studies and Observational Cohort and Cross-sectional studies, 14 criteria are used to evaluate the study quality, while for Case-Control studies 12 criteria are used. 11 criteria are used to determine the study quality of RCTs. This means that a maximum quality score of 11, 12 or 14 can be achieved depending on the study type. This quality score will be used to determine if the study should be included in the review. Quality scores are divided into 3 main categories: Good, Fair or Poor. See Table 2 for details.

* CD = Cannot determine, NR = Not reported, NA = Not applicable

Any studies that are excluded will be tracked with reasons for rejection.