Systematic reviews and meta-analyses are two forms of review articles in medical literature. Working as a medical writer means you’re expected to source the best available medical evidence that reflects current healthcare practice.
We’ve looked at how to use medical journal search engines to find medical literature for a health topic. However, search results can produce a broad range of different studies with conflicting results for a clinical question (hypothesis).
Reviews articles are traditionally used to find summarised evidence on a particular topic.
When you’re sourcing academic medical and scientific literature, reviews are considered the first source of evidence you should read.
So how can you discuss reviews most effectively in your writing?
This article is the first in a four-part series on different types of clinical evidence. It helps you understand how both systematic reviews and meta-analyses can provide conclusive medical information.
First, let’s consider why reviews are thought to be a good source of evidence.
You may have heard of the hierarchy of evidence in medicine. The inverted pyramid suggests sourcing most of your evidence from the top downwards.
Reviews are considered the top of the hierarchy of evidence. They summarise the outcomes of various intervention trials and can be an efficient method of drawing conclusions in medicine.
This means health care decisions are not based solely on one or two studies.
Reviews ensure a whole range of research information available on any given health topic is taken into account.
Systematic reviews and meta-analyses are thought to offer more reliable synthesised data and findings.
The methods used to review many studies aims to limit bias or assumptions in health topics, allowing you to have greater confidence for drawing conclusions in medicine.
So, what is a systematic review?
As the name implies, a systematic review is a detailed and comprehensive search strategy of published literature for a clinical question (hypothesis).
The summary of the literature is a synthesis of all the relevant studies for a particular topic in medicine.
Searches are conducted using a variety of selection criteria based on a protocol designed by the reviewers to limit study bias.
When you’re sourcing systematic reviews to use in your writing, you should look for reviews that:
- Define what types of studies were included and excluded. Such as whether the review includes only randomised-controlled trials (RCT), published studies, etc
- Have a clearly defined, explicit question
- Assess the quality of studies selected
- Have a transparent, reproducible strategy for screening and including studies, including a documentation of decisions
- Indicate the types of interventions used and control groups
- Discuss any bias and limitations of the review
- Include a meta-analysis
What is a meta-analysis?
A meta-analysis is often, but not always, included in a systematic review. However a meta-analysis can be published without including a systematic review and this is where is can get confusing.
What’s important to understand is that meta-analyses and systematic reviews complement each other.
A meta-analysis uses statistical techniques to synthesise the large amount of data from a systematic review into a single quantitative summary.
The data obtained in a meta-analysis is used to demonstrate the magnitude of effects an intervention has between two variables.
The benefit of a meta-analysis is the pooled sample size is increased, which improves the statistical power of the analysis and treatment effect.
The treatment effects of a meta-analysis can be measured statistically by:
- Odds ratios (OR)
- Weighted or standardised means differences
- Relative risk or risk ratios (RR)
- Confidence intervals (CI)
- Forest plot
A good meta-analysis includes:
- Reproducible data extraction
- Appropriate analysis and reporting of results
- Interpretation of the findings that is supported statistically with data
- Implications for future research, such as for health policy or clinical practice
Where can you source systematic reviews and meta-analyses?
The online Cochrane library is a widely recognized and respected source that disseminates systematic reviews and meta-analyses.
You can search the Cochrane database of systematic reviews for reviews on the efficacy of interventions in medicine.
You can also search known medical databases, such as Medline, PsycINFO and EMBASE for systematic reviews for information from studies on diagnosis, aetiology or prognosis in health and medicine.
Published review studies will often mention in the title that the study represents a systematic review or meta-analysis.
Looking for the word ‘review’ in the title can help you select systematic reviews or meta-analyses from a list of search results.