Chapter 2 – Meta-analysis 33 Methods Protocol and registration The protocol for this study was pre-registered on ClinicalTrials.gov (ID: NCT04387851) and conducted based on the PRISMA statement (Appendix A) and Cochrane recommendations (2020). The protocol was registered based on a single search strategy for both nocebo and placebo studies, which, due to the volume of the studies returned, is now divided in two separate papers. Here, we report only the nocebo (arms of) experimental studies. Databases and selection criteria PubMed, PsycINFO, EMBASE, and the Cochrane CENTRAL Methodology Library were searched to identify studies. Languages were a-priori restricted to English, Dutch, and German and the publication period was not restricted. Searches were initially conducted on March 18th, 2019. Repeated searches for studies published after this time were conducted in June 2020 and July 2021. The detailed key-word strategy for each database will be made available online upon publication (Appendix B). We searched for original, peer-reviewed, controlled experimental studies (or study arms) on healthy human participants that aimed to experimentally induce placebo and/or nocebo effects. Patient samples were not included, to improve the homogeneity of the results, and for the same reason we focused on cutaneous sensations (i.e., pain and/or itch stimulations that were administered on the skin), excluding for
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