7. How do the reported results compare with previous studies?
The strongest evidence about whether an intervention is useful and safe consists of results from several studies by different investigators. Rarely does a single study provide a final, definitive answer. There is a need for a study to be replicated, which involves repeating a study using the same methods but with different volunteers and investigators. Replication of a study gives more confidence that the results are reliable and valid. In addition, independent evaluations that compile the results of multiple studies and rigorously assess the quality of the data from them are especially useful. These evaluations are called systematic reviews and meta-analyses.