In evidence-based medicine, scholarly literature is grouped by the presence or absence of critical appraisal. Critical appraisal is the process of assessing and interpreting research by systematically considering its validity, results, and relevance. Research that has been critically appraised is labeled Pre-appraised (a.k.a., Filtered and Processed). Research that has not been critically appraised is labeled Non-Appraised (a.k.a., Unfiltered and Non-Processed).
Generally, primary literature is Non-Appraised at the individual article level. Secondary literature is sometimes Pre-Appraised. Examples of Pre-Appraised evidence include, Systematic Reviews, Meta-Analysis, Critically Appraised Topics, and Clinical Guidelines. Please note that traditional Review articles, which are secondary in nature, are not Pre-Appraised.
Pre-Appraised sources of evidence are not available for every clinical situation. When this type of evidence is not available on a situation/topic, primary literature must be identified and critically appraised by the clinician (follow the EBM practice Model).