[Music] if you're interested in systematic reviews it won't be long before you see a forest plot why do we need forest plots let's say you study headaches and you want to know which medication is more effective the drug most doctors recommend or a newer drug to answer that question using a systematic review you look at thickets and thickets of research and narrow that research down to the most relevant studies now what you need some way to quickly display what each study has to say and show what you found when you combine the results that's what a forest plot is for want to make a forest plot start by creating a vertical line this line is known as the line of no effect it splits your plot into two sections on one side you'll put studies that say the newer drug is more effective on the other side put the studies that say the standard drug is more effective studies that show a big difference between the two drugs you place further away from the line studies that show not much of a difference put them closer to the line and studies that don't show a difference are on top of the line let's take a closer look at the studies the square in the middle shows the study result in other words what the study discovered when it compared the headache medicines the size of the square basically reflects the size of the study but how sure are we about these study results that's why we need this line it's called the confidence interval the longer the line the more unsure the researchers were about the difference between the two drugs that's why a forest plot is so useful you can take studies that have uncertain results and put them together to form a story that story might tell you that the newer drug is more effective than the standard drug the newer drug is less effective or the results are mixed and you might need to do some more investigation whatever the story is you can get a good sense of what the studies to say just by looking at a forest plot but for a more precise idea you'll need to summarize the results or do what's known as a meta-analysis how do you do that it involves calculations which we won't get into right now but a simple explanation is you average the studies giving a bigger weight to the bigger studies to create a weeded average that tells you which drug is more effective at least according to the studies you found and that's how you use a forest plot so now when you see something like this don't panic just start with the trees and eventually you'll see the forest [Music] you [Music]