Systematic Reviews

Original Editor - User Name

Top Contributors - Stefano Berrone and Angeliki Chorti  

Introduction

A systematic review is a tool of quantitative research methodology that, through a systematic search and analysis of the literature, aims to answer to a research question. In fact, after identyfing all the literature relevant for contents and study design, it collects and analyses data from the studies included in the review. A systematic review can include a meta-analysis, that allows to synthesize the quantitative data from the studies included into a single statistical analysis. The presence or not of a metanalysis depends mostly on the homogeneity and quantity of the studies.

Steps of a systematic review

The following list reports the main steps of the process of carrying out a systematic review.

- Research question As for every work of research, is the research question that guides the choice of the paradigm and of the methodology of research. The research question can come from a dilemma inherent to the clinical practice, a gap in the practical or theorethical knowledge, or a mix of these elements. The systematic review is an approach that can be included in quantitative methodologies, because it shares the main features of this methodology, such as hypothesis testing, numerical data collection and analysis and the role of the researcher detached from the research.

- Search strategy The search strategy is the way in which the researcher runs the elctronic search to select the articles to include in the review. There is not a list of search strategies among which we can choose one. In fact, a systematic review is supposed to describe in details the search strategy that was used, as it influences the quality of the study. The most important elements of a search strategy are:

- balancing sensitivity and specifity. Where sensitivity means finding a high proportion of relevant studies, and specificity means finding a low proportion of irrelevant studies.

- selecting databases (the presence of a thesaurus improves the coverage)

- identifying MeSH terms to search, related to the research question or research framework (for example PICO).

- using database-appropriate syntax (for example parentheses, Boolean operators, field codes, variations in search terms)

Moreover, a search can also include other actions rather than electronic database search, such as reference lists checking and direct searching on key journals.

- Inclusion and exclusion Inclusion and exclusion criteria interest the contents of the studies selected and their design. For the contents the PICO (Population, Intervention, Comparison, Outcomes) framework can be used. It summarizes the main components to consider when selecting studies. On the base of the objectives of the research, the researcher puts some inclusion and exclusion criteria for each of these components. The PICO framework is a useful tool for the inclusion/exclusion startegy, but it is not mandatory, as there are other strategies that are effective (for example the SPIDER framework for qualitative evidence synthesis). It is up to the researcher to adopt the most appropriate strategy for the research question. About the study design, the researcher decides a priori what types of studies to include and exclude, for example RCT, quasi experimental trials, cohort studies or combinations of them. More criteria can be added, for example language restrictions, free-acces studies, or published versus unpublished studies.

After having obtained a list of titles and abstracts, the studies that meet inclusion criteria are then reviewed in full. To ensure inter-rater reliability the review process has to be done by two or more researchers. All reviewed studies should be recorded with thier own reasons dor inclusion and exclusion.

- Data extraction The data extraction follows the identification of eligible studies. The aim of this step is to gain information about the included studies, and, in the case of a metanalysis, to obtain the quantitative data to carry out the statistical analysis. The information to be extracted from the studies are choosen by the researcher. The goal is to provide all the information necessary to generalise the results.

- Quality assessment A systematic reviews evaluates the quality of the studies included through a risk of bias assessment. Different study designs have different risk of bias assessment tools. Here some examples of tools that can be used for three study designs:

- RCT: Cochrane Risk of Bias tool (ROB)

- case control studies: JBI Checklist for Case-Control Studies

- cohort studies: CASP- Cohort Studies

Systematic Reviews and physiotherapy

Systematic reviews have a relevant role in evidence based practice because they are on the top of the pyramid of evidence. Therefore, the results can be used to guide evaluation and treatment choices in routine physiotherapy practice. As the results and conclusion of systematic reviews in physiotherapy are often not net and exclusive mostly due to the heterogeneity of studies, as a user of research it is important to analyse and interpret the all the information given by the systematic review. In fact, we can gain useful information for evidence based practice from the whole process of research of a systematic review, for example from the research question that identifies a gap in the knowledge and from the presence or not of studies on a topic and from their quality. Moreover, systematic reviews in physiotherapy are useful to have an impartial view about treatments and intervention, that is more difficult to keep when we read and analyse single studies.