The following image represents the hierarchy and availability of the different types of research evidence and studies. As you can see, Systematic Reviews and Meta-Analysis are the highest level of evidence, but the least populous of all the study types.
View the following presentation for a brief introduction to the EBM Cycle
Guidelines for strict clinical systematic reviews do not always work well for the fields of nutrition, public health or mental health. It is worthwhile, however to be familar with those guidelines and then modify the searching and the types of studies included to fit these disciplines. See the Guides for Writing Systematic Reviews box to the left.
There are guides for systematic reviews in non-clinical topics such as nutrition and public health reviews. You can see these on one of our other systematic review guides, Systematic Reviews for Nutrition and Public Health.
Remember the evidence pyramid and how few systematic reviews and meta-anaylses there are? This can be attributed to a few factors:
The Cochrane Collaboration estimates about a year to complete the process, and this is often by teams of people working together on one review.