PRISMA-P checklist.

Title: Preferred Reporting Items for Systematic review and Meta-Analysis Protocols (PRISMA-P) 2015 statement. Legend: This file contains the PRISMA-P (Preferred Reporting Items for Systematic review and Meta-Analysis Protocols) 2015 checklist: recommended items to address in a systematic review protocol. The checklist is available at <a href="https://doi.org/10.1186/2046-4053-4-1" target="_blank">https://doi.org/10.1186/2046-4053-4-1</a> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0300076#pone.0300076.ref039" target="_blank">39</a>]. (PDF)