Armed with a well-built clinical question, a clinician proceeds to identify and obtain an answer from the evidence found in health literature. There are thousands of health information resources are currently available. Therefore, an understanding of the essential value of each resource type is required to determine when each one can best be applied.
Primary literature is where researchers publish their findings first. In the health field this is primarily in the form of journal articles outlining methodology, data, results, and conclusions. The evidence-based approach emphasizes a hierarchy of evidence based on study types. When searching for single studies on a topic, clinicians should utilize database tools (limits and filters) to obtain the highest level of evidence to answer a clinical question.
Examples: Randomized Controlled Trials, Cohort Studies, Case-Control Studies, Case Reports, Qualitative Studies
Secondary literature summarizes the primary studies by appraising the relevant individual studies to answer a particular clinical question. In most cases, clinicians should initiate a search for evidence-based answers to clinical questions with the secondary literature.
Examples: Systematic Reviews, Meta-Analyses, Evidence-Based Guidelines, some clinical database entries
There are now several online health information sources that accumulate the research (evidence) on clinical topics from the primary and secondary literature. These often provide an efficient way for clinicians to get up to speed on unfamiliar topics and fill holes in their knowledge base. However, a good clinician knows how to critically appraise and evaluate the primary and secondary literature.
Examples: DynaMed, UptoDate, most Guidelines and Society Statements, most Clinical Database Entries, Clinical Textbooks, Narrative Reviews
The definition of EBM states the importance of obtaining the "best available evidence." The evidence hierarchy is an attempt to rank the health information resource/study design with the highest quality sitting atop and the lower levels descending below. This hierarchy is helpful to guide evidence acquisition (literature searching) as well as providing clearer communication when discussing the landscape of health literature.
When it comes to prioritizing the evidence in any specific situation, clinicians will need understand the nuances of the evidence (reviews, studies) obtained. It is not uncommon for lower levels of evidence on the hierarchy to provide better evidence that those sitting above: a hot-off the-press large RCT over an older meta analysis containing small studies.