Rapid Review vs. Systematic Review: What are the differences?
There is increasing movement towards evidence-informed decision making for health policy and systems. Systematic reviews have been commonly used to inform policy decisions and health systems. A systematic review, however, is usually very resource intensive and takes about 12-24 months to complete. In the real-world setting, policymakers, health system managers and implementers are often faced with situations where they have a short timeframe to identify and review policy or program options to make decisions. Lack of timeliness poses a strong barrier to the use of evidence synthesis in health policy-making. Rapid reviews have emerged as an alternative to address this issue.
Rapid reviews can be viewed as a simplified approach to systematic reviews. A rapid review follows most of the principle steps of a systematic review, using systematic and transparent methods to identify, select, critically appraise and analyze data from relevant research. However, to provide timely evidence, some of the components of a systematic review process are either simplified or omitted. There are various approaches for simplifying the review components, such as by reducing the number of databases, assigning a single reviewer in each step while another reviewer verifies the results, excluding or limiting the use of grey literature, or by narrowing the scope of the review. In general, a rapid review takes about four months or less.
Timeliness and a reduced requirement of resources are the main benefits of a rapid review, which makes it more compelling for health program managers and policymakers. Nevertheless, rapid reviews also come with challenges. It is not easy to meet the time-sensitive needs of policymakers while maintaining methodological rigor and ensuring the validity of the review. Rapid reviews are considered more susceptible to bias compared to systematic reviews, although the extent of bias is unknown. Despite gaining interest from decision makers and program managers, rapid reviews receive criticism, especially from stakeholders in academia. This type of review is often viewed as a “quick and dirty” method, and therefore poses concerns about the reliability and validity of the results.
The distinction between rapid reviews and systematic reviews leads to a question of when to use or not to use a rapid review for evidence synthesis. Rapid reviews have been found to be useful in both emergency (e.g., epidemic, disaster relief) and non-emergency situations. However, there are situations where a rapid review may not be appropriate. For example, in a situation where the evidence will be used to inform the decisions or the development of guidelines that will be implemented at a very large scale (e.g., international, regional), a full systematic review is preferable to a rapid review. Thus, rapid reviews should not be viewed as a method to replace other evidence syntheses, but rather as a means to complement them.