What Research Methods Are Used in Evidence-Based Practice? Evidence levels in healthcare research can be classified into four categories based on the credibility of the material. Eastern Illinois University, "Why Is Evidence-Based Practice In Nursing So Important?" December 10, 2018: https://learnonline.eiu.edu/articles/rnbsn/evidence-based-practice-important.aspx These four categories, from most believable to least credible, are as follows: Trials that are randomised and controlled Evidence from cohort studies, case-control studies, or observational studies Expert viewpoints backed up by experience, studies, or reports Personal knowledge Any of these sorts of healthcare research can provide important information, but you should endeavor to make judgments based on the most trustworthy knowledge available.