Doing a comprehensive literature review is usually a part of any research process. When you start with your study, you first need to perform a thorough review of previous research so you can build on what is already available. However, it can sometimes be confusing when you hear different terms regarding literature reviews being tossed around. For instance, what is the difference between a literature review, systematic review and meta-analysis?
The terms are sometimes used interchangeably. In some cases, there does not appear to be a clear consensus about the exact differences. Here, we will briefly explain some of the characteristics of the three most commonly mentioned types of literature reviews.
Systematic Review is a synthesis of the existing studies and investigations (published and unpublished) that focus on a certain research question. It usually includes only quantitative studies although some sources suggest that it can include both quantitative and qualitative studies. This type of review aims to overcome possible biases by following a strict method. The time frame within which the literature was selected is usually defined (for example, you can focus on studies that were published between 2007 and 2016). Once you have predetermined your timeframe, relevant studies within that period are selected and evaluated for their validity. Your findings and data are then synthesized and interpreted.
Meta-analysis is a form of systematic review. It combines the findings of multiple scientific studies and statistically analyzes them. This method is based on a premise that similar studies will have a common truth, but that individual studies have a degree of error. Therefore, by combining the studies and applying statistic methods, you reach a higher statistical power than you would with a single study.
For this type of analysis, studies that fit the research question are identified. The studies in a meta-analysis are usually quantitative in design, with a preference for randomized-controlled trials. It is important that the studies in a meta-analysis are very similar in their topic, hypothesis and design, so they can be aptly compared. Once determined the identified studies are synthesized, codified and entered into a quantitative database for statistical analysis. The result of the meta-analysis can, for instance, tell us about the efficacy of a certain approach or treatment.
Cochrane is considered the gold standard for meta-analysis. It is probably the most distinguished source of research that relates to medical sciences and can help practitioners make evidence-based decisions.
This type of literature review potentially provides the best evidence in the hierarchy of reviews. A note for those looking to publish: editors often lean towards accepting a meta-analysis article, as it will likely yield more citations for their journal (for more details on this subject, see the article on impact factor).
Integrative Review might be the least known form of literature review (at least is seems to not be mentioned as often as others). However, some consider it to be one of the most comprehensive methodological approach of reviews. It includes experimental and non-experimental studies, as well as data from theoretical literature (hence the name integrative or inclusive). It can be used to define concepts, analyze problems and review theories.
In integrative review, these six phases are followed:
- Preparing the guiding question (this determines which studies will be included).
- Searching or sampling the literature (searching different databases and, ideally, including either all relevant studies or a representative sample of studies dealing with the subject).
- Data collection (extracting data from the selected articles).
- Critical analysis of the studies that are included in the review (articles are assessed for their rigor and characteristics).
- Discussion of results (data from different articles are compared, identifying knowledge gaps and direction for future research).
- Presentation of the integrative review (data are presented clearly for the reader, using tables, graphs, charts).
There are a lot of similarities between a systematic and integrative review. Some consider the latter to be yet another form of systematic review, which can be performed when one cannot do a meta-analysis.
In short, the meta-analysis and the integrative review can be considered as two forms of systematic literature review. The first step of every meta-analysis is a systematic review. However, a systematic review doesn’t need to include a meta-analysis. While the meta-analysis and the systematic review usually focus on quantitative studies, integrative review often include a broader spectrum of research.
Sources/Further reading:
de Souza, M. T., da Silva, M. D., & de Carvalho, R. (2010). Integrative review: What is it? How to do it?. Einstein (16794508), 8(1), 102-106.
Forward, L., & Hobby, L. (2002). A practical guide to conducting a systematic review. Nursing Times, 98(2), 36-37.
Whittemore, R., & Knafl, K. (2005). The integrative review: updated methodology. Journal of Advanced Nursing, 52(5), 546-553.