2.1. Search Strategy and Selection Criteria

An SLR was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [7]. Systematic searches were conducted in the Embase and PubMed electronic databases for a period from database inception to 15 November 2021, and manual hand searches were conducted to identify relevant documents across the following HTA and regulatory agency websites: National Institute for Health and Care Excellence (NICE); Haute Autorité de Santé (HAS); Institute for Quality and Efficiency in Health Care (IQWiG); European Network for Health Technology Assessment (EUnetHTA); Canadian Agency for Drugs and Technologies in Health (CADTH); Pharmaceutical Benefits Advisory Committee (PBAC); US Food and Drug Administration (FDA); the European Medicines Agency (EMA); and Therapeutic Goods Administration (TGA).

The full search strategy is provided in Supplementary Data, Tables S1 and S2. Initial searches using key words relating to ITC techniques alone resulted in an excess of hits and, as such, an alternative approach was taken. In addition to key words based on ITC techniques, the revised search strategy included key words based on journal name and author name from a predefined list of methodological articles of ITCs. This list was developed from methodologically well-known and referenced peer-reviewed papers and grey methodological literature/reports (such as the technical support documents [TSDs] produced by the NICE Decision Support Unit [DSU]), recent publications, targeted searches of the peer-reviewed and grey literature, and reviews of reference lists of the articles identified (Supplementary Data, Table S3).

All articles identified through the searches were imported to Microsoft Excel; primary-level screening of titles and abstracts was conducted against predefined eligibility criteria. Duplicates were removed to evaluate the studies for full-text eligibility. Eligible studies included those containing information on the methods of ITC techniques that were written in English, while studies reporting the application of ITC techniques solely in the context of specific treatments were excluded. The SLR eligibility criteria based on the PICO (Population, Intervention, Comparator[s], Outcome[s]) framework is presented in Supplementary Data, Table S4). However, since the objective of this SLR was not to investigate specific treatments or diseases, the PICO framework was not considered sufficient, and additional inclusion and exclusion criteria were utilized (Table 1).

Additional search inclusion and exclusion criteria.

Abbreviations: ITC, indirect treatment comparison.