I am trying to do a meta-analysis research about the periphyton and epiphyton at the global scale to compare the biomass and other parameters. There were so many papers to read, does anyone have a standard method to choose the paper?
I highly recommend that you refer to the Cochrane Handbook for SR. They have a good section about narrowing your research question using inclusion/exclusion criteria. I also recommend repeating a detailed search using "limits". Here is the link
Its a good question indeed. Though the question was posted long ago, still I feel to answer it for the future curious readers who are planning to conduct meta-analysis.
Prior starting a meta-analysis, its better to know the PICO (P: Target population, I: Intervention, C: Comparison, O: Outcomes of interest) to ensure all key components. You can set some inclusion criteria to get only eligible studies. During literature search in the electronic databases, you need to careful while choosing keywords so that you get only relevant studies. You also can choose title and abstract for primary evaluation of studies. While searching the databases, you can exclude review articles, editorials, non-human studies and other non-relevant topic to minimize the number of studies. To exclude duplicate studies of different databases, you can use EndNote software. Hopefully, you can minimize the total number of studies by following these procedures.