With search results now obtained it is time to commence the critical appraisal process of judging the validity and quality of the papers. The decisions of which articles to include and exclude are based on the criteria specified in your protocol.
The screening process of your search results is done incrementally. The first stage is a screening of titles and abstracts, then a full-text analysis follows before data extraction. To reduce bias, you must have a minimum of two reviewers to screen.
Pre-screening: Record the numbers of results from each database or source recorded before screening commences.
Title and abstract screening: Each reviewer will need to scan titles and abstracts to see if they match the criteria or have some value to the systematic review. This is done separately by each reviewer to ensure minimal bias. The results are then compared.
Full-text screening: Multiple reviewers individually look through the full-text of included articles to fine-tune the final collection of articles that will contribute to the review.
The recording of the numbers of search results from each database should have occurred prior to screening the search results. The use of the PRISMA flow diagram can be utilised for this purpose.
The analysis of the papers is based on the reviewer assessing each against the inclusion and exclusion criteria as defined in the protocol. A systematic review will usually involve more than one reviewer, and each will need to provide a rationale for how the papers match the criteria or have some value to the systematic review. This is done separately by each reviewer to ensure minimal bias. The results are then compared.
Reviewers may utilise a checklist or table that will assist with the screening of articles. This documents each reviewer's rationale for selecting or rejecting the articles. This is 'cross-checked' to ensure all reviewers agree on the included articles.
The first phase of the analysis is to screen 'titles and abstracts' of papers against the eligibility criteria to determine articles that will be screened in the next phase. This is performed independently by each reviewer to reduce bias and reach an agreement on the selection of articles.
The second phase of the analysis is repeated to screen the full-text of papers against the eligibility criteria. This is performed independently by each reviewer to reduce bias and reach an agreement on the selection of articles. The remaining articles are those that will contribute to the review.
The critical appraisal process examines the validity, applicability and clinical importance of the studies before application to a patient. It is important to critically evaluate the literature to:
There are a number of checklists available to assist in the process of determining the quality of the studies. A checklist should be chosen to assess sources of bias that are likely to affect results in relation to the research question.
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