What is systematic review?
I see two parts here, the systematic bit and the review part. Review referring to the identification, gathering and use of data to address a research question and then the systematic part which refers to the way the process is conducted.
The centre for review and dissemination or CDR at the University of York provide guidance that outlines the aims and process of systematic review. They highlight 2 key points:
- the aim is to identify, evaluate and summarise the findings of all relevant individual studies, and in doing so making available evidence accessible to decision makers.
- The ability to combine the results of identified studies with the aim of drawing conclusions from a body of evidence. If done appropriately, and commonly via meta-analysis, this can provide a more reliable and precise estimate of an intervention’s impact.
So why is this important? We know decision making in healthcare should be informed by the best available evidence. This can be difficult however due to the sheer amount of information available, often heterogeneous, generated in different ways, with different levels of bias and therefore there is a risk that information is misinterpreted or uncertainty regarding which evidence is best used for decision making.
Systematic reviews allow for these complexities to be understood and to provide clarity, indeed, the CDR highlight that Systematic reviews use a strict scientific design based on explicit, pre-specified and reproducible method, so they are protocol driven (systematic), therefore these can provide reliable and defensible estimates and conclusions.
From an evidence perspective I see systematic reviews through a couple of lenses.
First, as a piece of evidence in its own right; a protocol driven, reproducible piece of research providing new insight and evidence.
Second, as a contribution to other evidence; an input into HTA, decision making or an economic evaluation.
Lastly, the CDR also highlight that as well as communicating what we know about an intervention, systematic reviews can also help identify what we don’t know – thus can be used to guide further research.
From a practical perspective, I think it’s also important to highlight that as they are protocol driven, these take considerable planning and with that resource and time to conduct. Additionally, if you are new to these, they seem quite daunting, one of the things that I found helpful in learning about these is the abundance of best practice, guidelines and checklists to help review teams produce a robust review.
In summary systematic review, is a really important process in HTA. It can provide robust research driven inputs into decision making by providing clarity and additional insight into the decision-making process.
- CDR. (2008). Systematic Reviews: CRD’s guidance for undertaking reviews in health care. Centre for Reviews and Dissemination
- Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. (2021) The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ 2021;372:n71