Finding, Critically Appraising, and Interpreting Evidence
Searching
Start by formulating an answerable question - population, intervention (the design feature), comparison, and outcome. Search using controlled vocabulary and synonyms across appropriate sources: PubMed/MEDLINE, CINAHL, PsycINFO, Scopus or Web of Science, and Google Scholar for citation chasing, plus grey literature such as the Center for Health Design's Knowledge Repository, the Facilities Guidelines Institute, national academy reports, and government agencies. Document the search so it can be repeated and updated.
Appraising
Judge each source on internal validity (was the design sound, were confounders controlled, was measurement blinded or objective), reliability, sample size and power, potential bias including funding and publication bias, and external validity - whether the population, setting, and culture resemble your project. A well-conducted qualitative study may be the best available evidence for questions about experience and behavior, so do not apply the hierarchy mechanically.
Interpreting
Interpretation is not passive summary. Triangulate: conclusions supported by multiple independent studies and consistent with plausible mechanisms are more defensible than a single dramatic finding. Weigh consistency, recency, and dose-response. Translate findings into a statement of what is likely true for this project.
Traps
Assuming randomized trials are always best or always possible; equating peer review with high quality; ignoring context fit (an adult ICU study applied to a pediatric clinic); confusing statistical with practical significance; cherry-picking evidence that supports a preferred design; and mistaking correlation for causation.
Rule of thumb
Grade every source on three axes - level of evidence, methodological quality, and applicability to your setting - and state your confidence explicitly (strong, moderate, weak) before carrying it into design.