About Systematic Reviews

Understanding the Differences Between a Systematic Review vs Literature Review

Medical and public health evidence can be analyzed and reported using different review methods. Each type of review has a specific place in the scientific literature, with its own benefits and challenges. The kind of review to be conducted depends on the intended purpose of the research. Literature reviews usually answer broad and descriptive research questions. Systematic reviews are more comprehensive and precise because they seek to answer specific scientific questions of high importance. The reason for their popularity is the transparency, thoroughness, and reduced risk of bias they provide, making them excellent tools for supporting evidence-based medical practice. You can read more about the development of a systematic review definition here. All the review methods attempt to summarize the available information on a particular topic. The principal difference in the review types lies in the methodology followed in each of them.

Let’s look at these differences in further detail.

Goal of the Review

The objective of a literature review is to provide context or background information about a topic of interest. Hence the methodology is less comprehensive and not exhaustive. The aim is to provide an overview of a subject as an introduction to a paper or report. This overview is obtained firstly through evaluation of existing research, theories, and evidence, and secondly through individual critical evaluation and discussion of this content.

A systematic review attempts to answer specific clinical questions (for example, the effectiveness of a drug in treating an illness). Answering such questions comes with a responsibility to be comprehensive and accurate. Failure to do so could have life-threatening consequences. The need to be precise then calls for a systematic approach. The aim of a systematic review is to establish authoritative findings from an account of existing evidence using objective, thorough, reliable, and reproducible research approaches, and frameworks.

Level of Planning Required

The methodology involved in a literature review is less complicated and requires a lower degree of planning. For a systematic review, the planning is extensive and requires defining robust pre-specified protocols. It first starts with formulating the research question and scope of the research. The PICO’s approach (population, intervention, comparison, and outcomes) is used in designing the research question. Planning also involves establishing strict eligibility criteria for inclusion and exclusion of the primary resources to be included in the study. Every stage of the systematic review methodology is pre-specified to the last detail, even before starting the review process. It is recommended to register the protocol of your systematic review to avoid duplication. Journal publishers now look for registration in order to ensure the reviews meet predefined criteria for conducting a systematic review [1].

Search Strategy for Sourcing Primary Resources

Literature reviews use published resources collected from specific databases. The search for primary studies is comprehensive but not exhaustive. In a systematic review, sources are collected from databases and multiple other sources such as blogs from pharmaceutical companies, unpublished research directly from researchers, government reports, and conference proceedings. These are referred to as grey literature. A search strategy is usually developed by formulating the research question, identifying key concepts, creating search terms (free-text terms and controlled vocabulary terms) and combining using Boolean operators, establishing search limits, and adapting search syntax for different databases.

Quality Assessment of the Collected Resources

A rigorous appraisal of collected resources for the quality and relevance of the data they provide is a crucial part of the systematic review methodology. A systematic review usually employs a dual independent review process, which involves two reviewers evaluating the collected resources based on pre-defined inclusion and exclusion criteria. The idea is to limit bias in selecting the primary studies. Such a strict review system is generally not a part of a literature review.

Presentation of Results

Most literature reviews present their findings in narrative or discussion form. These are textual summaries of the results used to critique or analyze a body of literature about a topic serving as an introduction. Due to this reason, literature reviews are sometimes also called narrative reviews. To know more about the differences between narrative reviews and systematic reviews, click here.

A systematic review requires a higher level of rigor, transparency, and often peer-review. The results of a systematic review can be interpreted as numeric effect estimates using statistical methods or as a textual summary of all the evidence collected. Meta-analysis is employed to provide the necessary statistical support to evidence outcomes. They are usually conducted to examine the evidence present on a condition and treatment. The aims of a meta-analysis are to determine whether an effect exists, whether the effect is positive or negative, and establish a conclusive estimate of the effect [2].

Using statistical methods in generating the review results increases confidence in the review. Results of a systematic review are then used by clinicians to prescribe treatment or for pharmacovigilance purposes. The results of the review can also be presented as a qualitative assessment when the end goal is issuing recommendations or guidelines.

Risk of Bias

Literature reviews are mostly used by authors to provide background information with the intended purpose of introducing their own research later. Since the search for included primary resources is also less exhaustive, it is more prone to bias.

One of the main objectives for conducting a systematic review is to reduce bias in the evidence outcome. Extensive planning, strict eligibility criteria for inclusion and exclusion, and a statistical approach for computing the result reduce the risk of bias.

Intervention studies consider risk of bias as the “likelihood of inaccuracy in the estimate of causal effect in that study.” In systematic reviews, assessing the risk of bias is critical in providing accurate assessments of overall intervention effect [3].

Conclusion

With numerous review methods available for analyzing, synthesizing, and presenting existing scientific evidence, it is important for researchers to understand the differences between the review methods. Choosing the right method for a review is crucial in achieving the objectives of the research.

References

[1] “Systematic Review Protocols and Protocol Registries | NIH Library,” www.nihlibrary.nih.gov. https://www.nihlibrary.nih.gov/services/systematic-review-service/systematic-review-protocols-and-protocol-registries

[2] A. B. Haidich, “Meta-analysis in medical research,” Hippokratia, vol. 14, no. Suppl 1, pp. 29–37, Dec. 2010, [Online]. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3049418/#:~:text=Meta%2Danalyses%20are%20conducted%20to

[3] C. E. Kennedy et al., “The Evidence Project risk of bias tool: assessing study rigor for both randomized and non-randomized intervention studies,” Systematic Reviews, vol. 8, no. 1, Jan. 2019, doi: 10.1186/s13643-018-0925-0.

Learn More About DistillerSR