Doublecheck

• AMSTAR, Amstar

Giving due weight to sources

• A relevant source is one where the topic is the same as for the statement you use it for. E.g. — if you're writing about methotrexate treatment for rheumatoid arthritis: the best possible source in one covering treatment options in general, or even specifically methotrexate. The second best is a source that is about a different treatment, but states your topic in passing: "DMARDs have benefits over methotrexate, which may cause leukopenia". Less relevant sources may be a paper on psoratic arthritis that mentions methotrexate as a treatment for RA. Entirely unrelated or marginally related sources should never be used.
• Quality assessment is performed according to the section on assessing evidence quality, but in essence means that higher quality sources trump lower quality sources — where the lowest quality sources should be entirely avoided.
• Medical research moves in fits and starts: sometimes.... with evidence changing from one year to the next. Major organizations often recommend reviews of the evidence be no older than 2 years in order to be deemed "best evidence" (providing they haven't been trumped by newer authoritative evidence) . Wikipedia employs a cutoff at 5 years, where anything older than that only being used in exceptional cases, such as rare diseases. Sources older than 10 years should not be used (not including certain related fields such as anatomy, where the body of knowledge moves far slower).
• Always seek the best source possible. It is unreasonable to expect editors to always use the best sources, but they should always try. Issues finding or using the best sources may be: pay-walls (see the Resource Exchange for help on accessing pay-walled content); difficulties in determining which source is the best; or it may just be unreasonably time-consuming to go through all possible sources.
  When you have several contenders for best possible source, and they don't agree on something make sure to give both viewpoints, but remember to avoid giving false balance

Try to avoid bias when selecting sources. Bias can arise from your search criteria and search tools, and in which sources you have access to (see for example FUTON bias).