You will occasionally want to look for information in what are sometimes called "unfiltered" resources. In these instances, you will need to use limits or refine your search to find certain publication types.
These are some of the publication types that are associated with higher levels of evidence. You may want to start at the top of the pyramid and work your way down.
Publication Types by Question Type: Different study types are suited to different questions. For example:
Most Clinical Questions: Meta-analyses, systematic reviews
Therapy: Randomized Controlled Trial
Diagnosis: Prospective, blind controlled trial compared to gold standard
Prognosis: Cohort study, case control, case series/case report
These are a few of the publication types associated with evidence-based practice taken from the Glossary of EBM Terms from the Centre for Evidence-Based Medicine Toronto and from the MeSH Database http://www.ncbi.nlm.nih.gov/mesh
Meta-analysis: A systematic review that uses quantitative methods to synthesize and summarize results of studies. The meta-analysis refers to the statistical compilation of homogenous studies.
Systematic Review: A summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies. This study may or may not include a meta-analysis.
Randomized Controlled Trial: A study in which participants are randomly allocated into an experimental group or control group and followed over time for the variables/outcomes of interest.
Cohort Studies: Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics.
Case Controlled Studies: A study which involves identifying patients who have the outcome of interest (cases) and patients without the same outcome (controls), and looking back to see if they had the exposure of interest.
Case Series: A report on a series of patients with an outcome of interest. No control group is involved.