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Types of reviews

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Writing a literature review in some form is commonly part of a PhD. Literature reviews can have a variety of purposes, and use different search strategies. The review can be a part of the introduction of an article-based dissertation, or a chapter in a book-type dissertation. Some PhD students may write a systematic review as part of their PhD project.

“Systematic reviews and narrative reviews serve different purposes and should be viewed as complementary. Conventional systematic reviews address narrowly focused questions: their key contribution is summarizing data. Narrative reviews provide interpretation and critique; their key contribution is deepening understanding.” (Greenhalgh, Thorne, & Malterud, 2018, p. 2)

A review is an independent work of research in which the researcher examines the research question through the lens of literature. It may be a review of the literature with the aim of verification, i.e. demonstrating what is known in the field. Another possibility would be to create a review for research and examine what is not known and possible ways of exploring the unknown areas; in this way, the review has a generative aim (Hart, 2018).

On this page, you will learn about two main types of literature reviews. These types are often understood to be at either end of a continuum of reviews. The narrative review, which Hart (2018) terms scholastic, is intended to deepen the understanding of a body of literature. The systematic review has the potential of being interventionistic because it can aid in decision making in many areas and levels of society.

1. Narrative reviews
2. Systematic reviews

Narrative reviews

The narrative review is the classic literature review and is a long-standing tradition in research. Today it is the most common form of review in the humanities and parts of social sciences. The important contribution of a narrative review is the author’s interpretation and critique of the literature under scrutiny in the review.

A narrative review can examine many topics; one would expect the narrative reviewer to read widely and use literature from across subject disciplines. In this type of review, it would be possible, and maybe even expected, to include historical and philosophical perspectives. The literature included in such a review may be in any format; one can therefore include books and grey literature as well as journal articles. Investigation in a narrative review is iterative and for each re-reading of the literature the interpretation should be deepened. According to Hart (2018, p. 93), a good narrative review would challenge arguments, identify and resolve contradictions, challenge propositions, and reach its conclusions through reasoning, usually through a rigorous conceptual analysis.

Systematic reviews

The systematic review is a methodical approach in order to collect, appraise and synthesize all available research and data relevant to a predefined research question. In contrast to narrative approaches, systematic reviews are based on documented, transparent and reproducible searches, building on the same principles as other aspects of empirical research. They are predominantly used in evidence-based health care, medicine and the life sciences, but are increasingly being adopted in other academic disciplines like psychology, education and social science.

A broad definition of a systematic review is:
“A systematic review is a review of a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyze data from the studies that are included in the review. Statistical methods (meta-analysis) may or may not be used to analyze and summarize the results of the included studies.” (Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group, 2009)

The role of the systematic review is to examine the evidence across multiple individual studies with similar research questions to arrive at some conclusion about our previous knowledge. A systematic review ideally examines all previous research concerning the research question. The search methodology is extensive, and follows predefined rules. The common stages in a systematic review are:

  1. Clarifying a research question. A systematic review often starts with a focused research question.
  2. Searching. Before the search in relevant reference databases, one creates keywords to use in the searching. The search process is documented.
  3. Screening. One often starts out with hundreds or thousands of references, after searching the included databases. The researcher uses inclusion and exclusion criteria, which are clearly communicated as part of the methodology. In the first selection phase, the PhD researcher(s) uses the abstracts, in order to exclude the studies that obviously do not meet the inclusion criteria.
  4. Selecting. A final selection is made, based on the reading of the studies that were included after the screening phase. The amount of included studies has now finally been narrowed down. Often, but not in all types of systematic reviews, the researcher will make a quality assessment of the studies, including an assessment of risk of bias.
  5. Writing the review. In the writing of the review, the process of steps 1-4 is documented, a quality assessment of the evidence is conducted and the results are presented in a structured and lucid form.

The key in the systematic approach is, simply put, to predefine what you are looking for. Although you are looking for all previous research, there must be enough commonalities among the studies to make comparisons that will aid your conclusion. You will be looking for studies that address the same research question, have similar samples and sampling methods, involve similar interventions, expositions, experiments or techniques, and use similar research methods. The search will usually try to capture as much literature as possible that is relevant to the research question, while inclusion and exclusion criteria will be used to reduce the amount of studies and keep the relevant ones. Documentation of the search will make the review work replicable for other researchers. The quality assessment will help to determine the strength of the evidence.

Types of systematic reviews

The term systematic review covers a wide variety of reviews that are systematic in different ways, as exemplified in the following section.

The classic systematic review
The classical approach to systematic reviews aims to summarize and draw conclusions based on the research related to a research question. The material is previous original studies, both published and unpublished. The process requires two reviewers to perform the review. Importantly, the search strategy is reported, there are clear inclusion and exclusion criteria, and the included studies are quality assessed.

Within this classic category, slightly different principles and guidelines can be used, such as the Cochrane Collaboration or the NHS Centre for Reviews and Dissemination (Grant & Booth, 2009, p. 102). Statistical methods, or a meta-analysis using statistics to integrate results from several studies, may or may not be used in a systematic review (The PRISMA Group, 2009).

Umbrella reviews
An umbrella review is a synthesis of findings from several reviews. A quality assessment of the reviews is performed.

Scoping reviews
A scoping review is performed to gain an overview of a broad field, rather than detailed answers to specific questions (Moher, Stewart, & Shekelle, 2015). A scoping review provides a preliminary picture of the available research literature, through identifying the nature and extent of the research evidence (Grant & Booth, 2009). Ongoing research is often included. Typically, however, quality assessment is not performed. The scoping review shares some features with the systematic review, being systematic, transparent and replicable, but cannot be used to recommend policy or practice. As a scoping review can be used to identify research gaps, it is sometimes used as a method to decide whether a full systematic review is needed or not.

Scoping reviews are a relatively new but increasingly common approach for mapping broad topics (Pham et al., 2014). The method was developed by Arksey and O`Malley (Arksey & O’Malley, 2005; Daudt, Van Mossel, & Scott, 2013).

Meta-analysis
A meta-analysis statistically combines and analyses quantitative studies. The goal can be to integrate, summarize, or organize. The statistical data from the included studies will have a similar research question and methodology, which is necessary for the validity of the meta-analysis. In this way, “Small or inconclusive studies lacking in statistical significance can nevertheless make a contribution to the larger picture.” (Grant & Booth, 2009, p. 98). Note that not all studies using the meta-analysis method are systematic reviews.

Rapid reviews
A rapid version of the systematic review, based on the need for evidence-based decisions within a policymaker´s time frame. Some of the stages will be limited: “The methodology identifies several legitimate techniques that may be used to shorten the timescale. These include carefully focusing the question, using broader or less sophisticated search strategies, conducting a review of reviews, restricting the amount of grey literature, extracting only key variables and performing only ‘simple’ quality appraisal” (Grant & Booth, 2009, p. 100).

Qualitative systematic reviews
In recent years, we have seen an increased interest in conducting systematic reviews of qualitative research. A systematic review of qualitative research would usually be referred to as a meta-synthesis. There are several methods used for synthesizing qualitative research, and one of the best known is the meta-ethnography developed by Noblit and Hare (1988). A qualitative synthesis should be conducted using qualitative research methods (Malterud, 2017).

A more comprehensive list of review types can be found in Grant and Booth’s article from 2009.

Useful resources

As the field of systematic reviews has developed, useful resources have developed alongside it. We find handbooks and guidelines on the relevant methodology from specialist institutions such as the Cochrane Collaboration. In addition, there are databases and registries devoted to finding reviews and protocols for reviews in progress. Of special interest to review authors are reporting guidelines, as following these will increase the chances of having your review published.

Methodology, databases, protocol registries and reporting guidelines

Here we have collected well-known resources on methodology, reporting guidelines, databases and protocol registries.

Methodology

A number of manuals and handbooks have been written to help the researcher to create a well-developed systematic review.

Databases of systematic reviews

Systematic reviews may also be found in bibliographic databases. Here you can find them by searching extensively in several reference databases, utilizing the review filter, or by using the search terms “review”, “overview”, or “meta-analysis” in the title or abstract.

Protocol registries

In medicine and health, there are international registers of protocols for systematic reviews. These also record planned systematic reviews in order to prevent duplication of work.
A multilingual database of health evidence

Reporting guidelines

Many journals require the systematic review to be written in accordance with guidelines.

References

Arksey, H., & O’Malley, L. (2005). Scoping studies: towards a methodological framework. International Journal of Social Research Methodology, 8(1), 19-32. https://doi.org/:10.1080/1364557032000119616

Booth, A., Sutton, A., & Papaioannou, D. (2016). Systematic approaches to a successful literature review (2nd ed.). Los Angeles, CA: Sage.

Daudt, H. M. L., Van Mossel, C., & Scott, S. J. (2013). Enhancing the scoping study methodology: A large, inter-professional team’s experience with Arksey and O’Malley’s framework. BMC Medical Research Methodology, 13(1). https://doi.org/10.1186/1471-2288-13-48

Foster, M., & Jewell, S. (2017). Assembling the pieces of a systematic review : a guide for librarians. Lanham, Maryland: Rowman & Littlefield.

Grant, M. J., & Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information and Libraries Journal, 26(2), 91-108. https://doi.org/10.1111/j.1471-1842.2009.00848.x.

Greenhalgh, T., Thorne, S., & Malterud, K. (2018). Time to challenge the spurious hierarchy of systematic over narrative reviews? European Journal of Clinical Investigation, e12931. https://doi.org/10.1111/eci.12931

Haraldstad, A. M., & Christophersen, E. (2015). Literature searches and reference management. In P. Laake, H. B. Benestad, & B. R. Olsen (Eds.), Research in medical and biological sciences from planning and preparation to grant application and publication (pp. 125-166). Amsterdam: Elsevier.

Hart, C. (2018). Doing a literature review: releasing the research imagination (2nd ed.). Los Angeles, CA: Sage.

Malterud, K. (2017). Kvalitativ metasyntese som forskningsmetode i medisin og helsefag. Oslo: Universitetsforlaget

Moher, D., Liberati, A., Tetzlaff, J., & Altman, D. G. for the PRISMA Group (2009). Preferred reporting items for systematic reviews and meta-analyses: The PRISMA statement. PLoS Medicine 6(7): e1000097. https://doi.org/10.1371/journal.pmed.1000097

Moher, D., Stewart, L., & Shekelle, P. (2015). All in the family: systematic reviews, rapid reviews, scoping reviews, realist reviews, and more. Systematic Reviews, 4(1), 183. https://doi.org/10.1186/s13643-015-0163-7

Noblit, G. W., & Hare, R. D. (1988). Meta-ethnography: synthesizing qualitative studies. Newbury Park, CA: Sage Publications.

Pham, M. T., Rajić, A., Greig, J. D., Sargeant, J. M., Papadopoulos, A., & McEwen, S. A. (2014). A scoping review of scoping reviews: advancing the approach and enhancing the consistency. Research Synthesis Methods, 5(4), 371-385. https://doi.org/10.1002/jrsm.1123

Young, S., & Eldermire, E. (2017). The big picture: finding, evaluating, and applying systematic reviews across disciplines. In M. Foster & S. Jewell (Eds.), Assembling the pieces of a systematic review : a guide for librarians (pp. 13-29). Lanham, Maryland: Rowman & Littlefield.

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