Introduction: What is a meta-analysis?

Meta-analysis is a method which can be used to combine the results of two or more studies. But why should we want to do this?

In research, studies are conducted to try to answer questions about the clinical effectiveness of a treatment or intervention.

In some medical areas such as cancer and cardiovascular disease, several studies may have been conducted which have assessed the effectiveness of a particular treatment. These studies will have asked whether, for example, does treatment A provide significant benefits over treatment B in a particular group of people?

Although these studies have all assessed the same treatment comparison, the size of the benefit from these studies will vary either due to differences in study protocols or purely by chance. Some studies may find that treatment A is beneficial whilst others find it has no apparent effect or is even harmful. Therefore it can be useful to combine the results from these studies together to get a single answer about whether treatment A is more beneficial than treatment B.