Among individual primary research study designs, which is generally considered to provide the highest level of evidence?

Among individual primary study designs, the randomized controlled trial (RCT) is generally considered to provide the highest level of evidence, due to randomization minimizing selection bias and confounding. (Systematic reviews and meta-analyses of multiple RCTs sit even higher in the overall evidence hierarchy, since they synthesize findings across multiple RCTs, but among single primary study types, the RCT is the top tier.)