Not all systematic reviews of quantitative evidence allow one to complete a meta-analysis, as that is a statistical tool that has rules which must be met. A meta analysis does not apply to systematic reviews of qualitative or text/opinion evidence .
I agree with the above a systematic review is a collation of all the evidence on a particular topic through the best available RCTs and if not available case reports and series, the meta-analysis is the statistical method by which the treatment effect or desired outcome can be measured.
A systematic review of quantitative evidence does not have to only consist of RCTs. There are many valuavle questions to be answered through a SR that do not have the evidence base of an RCT.
A systematic review is a detailed, systematic and transparent means of gathering, appraising and synthesising evidence to answer a well-defined question.
A meta-analysis is a statistical procedure for combining numerical data from multiple separate studies. A meta-analysis should only ever be conducted in the context of a systematic review.
Conducting a meta-analysis would be a bad idea if your studies are too different to combine. Imagine you are conducting a systematic review on the effect of listening to music while studying on children’s exam performance and you find one study on classical music, two on pop music including primary school children and teenagers respectively, another on death metal and a fifth on 80’s synth classics. Would you combine these in a single meta-analysis or would you decide that the interventions (music type) and populations (age of children) are too dissimilar to combine and opt for a narrative synthesis instead? Deciding which studies you can and cannot combine in a meta-analysis will depend on the question you are asking and you should define the process for deciding in advance in your review protocol.
Conducting a meta-analysis may not always be sensible – even if you set out to do one. By specifying your approach to meta-analysis in advance, you can reduce the possibility of introducing bias and avoid making decisions retrospectively based on the studies or results you find. This is why spending time on your protocol and thinking through the analytic approach before beginning your systematic review is time well spent.
Reference: http://meta-evidence.co.uk
In systematic review we will answer research question by collecting and summarising all empirical evidence that fits pre-specified eligibility criteria. In the case of meta-analysis we will take the data of the identified evedences to summarise the results of these studies by using different statistcal methods.
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