Systematic reviews and meta-analyses are a distinct type of empirical studies – they use other, original empirical studies as their “sample,” to summarize their findings (i.e., evidence) related to a particular topic or intervention. The idea behind a systematic review is to make sure that an analysis of empirical literature on a specific topic is as comprehensive and unbiased as possible: it uses a deliberate and precise search strategy, includes all relevant studies meeting specific criteria, and takes their features and methods into account when summarizing their findings. For example, if we are interested in whether family therapy interventions for juvenile delinquents prevent further involvement in crime, a systematic review of all relevant empirical studies on such interventions would be very helpful, especially if it summarizes their results by giving more weight to the findings of more rigorous studies (the ones with random assignment to treatment and control groups, 1 larger samples, and longer follow-up periods for tracking recidivism outcomes).