Meta-analysis
A study that statistically combines the results of multiple independent trials on the same question, generally considered stronger evidence than any single trial alone. Several of this site's studied-dose citations are meta-analyses covering dozens of underlying trials and thousands of participants.
Example
A 2013 meta-analysis of 19 randomized trials and 1,683 subjects is the basis for melatonin's cited 0.5-5mg studied dose range for sleep-onset effects.