You are now nearly ready to write up the systematic review. You have reviewed the full text versions of any references that looked promising for inclusion, culling out those that were inappropriate (remembering to record reasons and numbers). You have read the references that have been selected and are sitting down ready to write about the subject.
For an initial systematic review, it is acceptable to tabulate the relevant data and discuss it, without performing any further analysis. This is a purely descriptive approach and although you will provide your writing groups opinions on the results, you may not want to do any further analysis. However, to get the most out of a systematic review you will probably want to go further. This could involve one of two approaches, either a meta-analysis or a narrative synthesis.
What is a meta-analysis?
If the references detail studies that are similarly designed, with similar duration, populations and study drug/intervention use, then a meta-analysis is possible. Meta-analysis are typically used in medicine and are a statistical approach to estimating the treatment effect. By combining a number of different studies, larger populations can be explored and this can provide insight into rare complications or adverse events, or provide a better overview of clinical efficacy. A good introduction to what a meta-analysis is can be found here.
What is a narrative synthesis?
If the references all include very small study populations, or the study designs are different, for example the study lengths vary widely, then a narrative synthesis may be more appropriate. This approach involves the identification of themes and trends in the research, highlighting aspects that appear to influence outcomes or are important for the intervention. A good introduction to what a narrative synthesis is can be found here.
Do you have any tips of writing a good systematic review?
First off, write the manuscript with the PRISMA checklist next to you, to ensure that all the information that it requires is included. Also, even though it may appear that the conduct of a systematic review is rigid and does not allow any creativity it is important that the final manuscript is not overly dry, otherwise no-one will read it and it is wasted effort. Ensure that the story of why the systematic review was conducted is included and that each step or question builds logically from the previous one. You do not want to make any sudden jumps, as although you may find them intuitive, your readers quite likely will not. They have not been immersed in the review and discussions around it. To avoid this, you should get a colleague who has not been involved in any discussions about the systematic review at any point to review a near-final draft. They are likely to identify any gaps in the narrative and you should listen to them and if you disagree you discuss your reasons with that person. Also, don’t forget to thank them in the acknowledgements.