Systematic Review: Develop question & key concepts, inclusion & exclusion criteria

At the heart of your systematic review is the research question that you are trying to answer. (A systematic review is an in-depth attempt to synthesise the evidence to answer a specific, focused question in a systematic way). It can be challenging to formulate the ‘right’ question for your topic, but the question will guide your search strategy and data analysis, so it’s very important to figure it out early in the process. Ask yourself if your question:

• Is answerable

• Is specific and focused

• Has not (recently) been answered by anyone else

Three types of questions were proposed by Eldredge (2002, p. 10). These types can also be related to more clinical questions:

• Etiology - Factors that predispose a population toward a certain condition (Why does D change with E in population F? Or What causes D to change in population F?).
• Prediction - Likelihood of a condition in a population (Will X affect Y? Or How will X affect Y? Or How will X progress over time?).
• Intervention - A therapeutic measure to address a condition in a population (Will J perform better than K at achieving outcome L?).

There are a number of different search mnemonics or frameworks you can use to identify the key concepts of a research question. 'PICO’ is the most well known (Richardson et al., 1995).

P - patient/problem/population

I - intervention 

C - comparison/control

O - outcome

There are also variants of PICO that prompt you for other concepts, such as time (PICOT), research type (PICOR) or study type (PICOS).

Other frameworks:

• ECLIPSE - Expectation/Client group/Location/Impact/Professionals/Service (evaluating services) (Wildridge & Bell, 2002)
• SPIDER - Sample/Phenomenon of Interest/Design/Evaluation/Research type (qualitative studies, especially with samples rather than populations) (Cooke et al., 2012)
• SPICE - Setting/Perspective (or Population)/Intervention/Comparison/Evaluation (evaluating outcomes of a specific intervention) (Booth, 2006)

Now that you have developed your question you must convert this research question into a format that is searchable in a database. While there are usually between 2 and 4 key concepts in your research question, these may not all be included in your search strategy.

An important characteristic of a systematic review is that the search is replicable; someone else should be able to follow the strategy and end up with the same articles. It’s very easy to look at an article and decide that you want to include it in your study, because the results look good, you’ve heard of the authors, or any other factors. To eliminate these personal biases as far as possible, it’s crucial to develop clear inclusion and exclusion criteria at the outset for your SR protocol. It may be useful to consider core outcome measures used in research in the field that you are reviewing when developing this criteria.

Some examples of criteria you might wish to consider include:

• Language of publication:  Ideally a systematic review search strategy would be conducted without language restrictions.   Best practice (if limiting by English language) would be to exclude at the full-text screening stage. See this article for tips on Google translate.
• Year of publication:  You need to justify any date limit included in a systematic review. 
• Human studies:  If you limit your search to human studies only, it is best practice to identify animal-only studies first, and then exclude those from the search results. See Cochrane Handbook Technical Supplement to Chapter 4 (p.60) for detailed information.
• Age groups:  Combinations of subject headings and keywords should be used to reliably retrieve age-specific studies, including those that are not indexed. Pre-tested filters may also be useful when investigating by age.
• Study design:  Always ensure that a study design restriction is appropriate for your SR topic. See this article by Burns et al. (2011) on levels of evidence.