First, CochraneHandbook recommends keyword search. Second, because no matter how many theories are ineffective in practice, we can practice them in PubMed database to see what is the difference between keyword search and free word search.

In meta-analysis, it is really necessary to follow certain retrieval strategies. Usually, when publishing meta-analysis articles, retrieval strategies will be listed in particular to ensure the repeatability of the analysis. According to an example (correlation, polarization and anxiety among Hollywood producers: systematic review and meta-analysis, 20 16, Gastroenterology).