Systematic reviews, as opposed to review, which are opinions of scientists, look at a ton of studies on a given topic and then derive the conclusions from there. Systematic reviews are scientific studies made to discover patterns and find the truth. they also are transparent enough to let others follow the same path and test the conclusions.
In the news from below you will learn that pot, ie medical marijuana, is not that dangerous and it can be used to reduce pain. Several US states have started accepting it to be publicly used. also, swearing reduces pain too.
While systematic reviews are a good way to use studies of studies in order to get some valid conclusions, there is also the meta analysis. Meta analysis simply merges all the data from all studies in order to get the truth out. Systematic reviews check many studies and rule out those who won’t be deemed useful: