Introduction

There are some good reasons for doing a systematic review:

• They are useful to summarise a lot of small studies together, to achieve an overview before conducting a big randomised controlled trial
• They are cheap and safe to do
• They are useful to resolve controversy where there are conflicting studies.
• They are useful to explore reasons for different results. For instance, a meta-analysis might be a very good way to explore different dosing regimens of a drug, or why certain populations respond differently.