Comparison of traditional and systematic review of literature

Most of us are familiar with the terms systematic review and literature review. Both review types synthesise evidence and provide summary information. So what are the differences? What does systematic mean? And which approach is best ?

Systematic describes the reviews methods. It means that they are transparent, reproducible and defined before the search gets underway. Thats important because it helps to minimise the bias that would result from cherry-picking studies in a non-systematic way.

This brings us to literature reviews. Literature reviews dont usually apply the same rigour in their methods. Thats because, unlike systematic reviews, they dont aim to produce an answer to a clinical question. Literature reviews can provide context or background information for a new piece of research. They can also stand alone as a general guide to what is already known about a particular topic.

Interest in systematic reviews has grown in recent years and the frequency of systematic reviews in Google books has overtaken literature reviews [with all the usual Ngram Viewer warnings it searches around 6% of all books, no journals].

Lets take a look at the two review types in more detail to highlight some key similarities and differences .

Systematic reviews ask a specific question about the effectiveness of a treatment and answer it by summarising evidence that meets a set of pre-specified criteria.

The process starts with a research question and a protocol or research plan. A review team searches for studies to answer the question using a highly sensitive search strategy. The retrieved studies are then screened for eligibility using the inclusion and exclusion criteria [this is done by at least two people working independently]. Next, the reviewers extract the relevant data and assess the quality of the included studies. Finally, the review team synthesises the extracted study data and presents the results. The process is shown in figure 2.

The results of a systematic review can be presented in many ways and the choice will depend on factors such as the type of data. Some reviews use meta-analysis to produce a statistical summary of effect estimates. Other reviews use narrative synthesis to present a textual summary.

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If you have a clinical question about the effectiveness of a particular treatment or treatments, you could answer it by conducting a systematic review. Systematic reviews in clinical medicine often follow the PICO framework, which stands for:

Population [or patients]

Intervention

Comparison

Outcome

Heres a typical example of a systematic review title that uses the PICO framework:Alarms [intervention] versus drug treatments [comparison] for the prevention of nocturnal enuresis [outcome] in children [population]

• Systematic reviews follow prespecified methods
• The methods are explicit and replicable
• The review team assesses the quality of the evidence and attempts to minimise bias
• Results and conclusions are based on the evidence

Literature reviews provide an overview of what is known about a particular topic. They evaluate the material, rather than simply restating it, but the methods used to do this are not usually prespecified and they are not described in detail in the review. The search might be comprehensive but it does not aim to be exhaustive. Literature reviews are also referred to as narrative reviews.

Literature reviews use a topical approach and often take the form of a discussion. Precision and replicability are not the focus, rather the author seeks to demonstrate their understanding and perhaps also present their work in the context of what has come before. Often, this sort of synthesis does not attempt to control for the authors own bias. The results or conclusion of a literature review is likely to be presented using words rather than statistical methods.

Weve all written some form of literature review: they are a central part of academic research . Literature reviews often form the introduction to a piece of writing, to provide the context. They can also be used to identify gaps in the literature and the need to fill them with new research .

• Literature reviews take a thematic approach
• They do not specify inclusion or exclusion criteria
• They do not answer a clinical question
• The conclusions might be influenced by the authors own views

A quick internet search retrieves a cool 200 million hits for systematic literature review. What strange hybrid is this ?

Systematic review methodology has its roots in evidence-based medicine but it quickly gained traction in other areas the social sciences for example where researchers recognise the value of being methodical and minimising bias. Systematic review methods are increasingly applied to the more traditional types of review, including literature reviews, hence the proliferation of terms like systematic literature review and many more.

Beware of the labels . The terminology used to describe review types can vary by discipline and changes over time. To really understand how any review was done you will need to examine the methods critically and make your own assessment of the quality and reliability of each synthesis .

Review methods are evolving constantly as researchers find new ways to meet the challenge of synthesising the evidence. Systematic review methods have influenced many other review types, including the traditional literature review.

Covidence is a web-based tool that saves you time at the screening, selection, data extraction and quality assessment stages of your systematic review. It supports easy collaboration across teams and provides a clear overview of task status.