Studies may appear good, but there may be subtle flaws that are not readily identifiable to the lay reader or to someone who does not work in that field. Journals are expected to assess studies for quality before publication. This assessment, generally a ‘peer review’ process can vary considerably between journals. Journals can be ranked according to the quality of assessment. The principal journal ranking system is the ‘impact factor’ which is often quoted on the journal or its website. Academics can be ranked according to productivity and impact. The host institution may also be ranked. There may well, however, be studies published elsewhere that are of high standard.
The introduction of the internet has led to a proliferation of ‘internet-only’ or e-Journals which are easy to set up and which may have very dubious sources of research with limited or no peer review. Care should therefore be taken to check the source of any published paper.
Standard databases generally only include papers published in reputable journals. This means that a search on a database such as PubMed (or Medline), or Embase, may miss a significant number of quality articles from other journals but should exclude articles that may be unreliable.