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.

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.

Meta-analysis: A systematic review that uses quantitative methods to synthesize and summarize results of 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 and that uses appropriate statistical techniques to combine these valid studies.

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: Involves identification of two groups (cohorts) of patients, one which recieved the exposure and one which did not, and following these cohorts forward for the outcome of interest.

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.