Systematic Reviews

Cochrane Handbook of Systematic Reviews: Chapter 4.6 Selecting studies

Cochrane recommends, "Use (at least) two people working independently to determine whether each study meets the eligibility criteria, and define in advance the process for resolving disagreements."

Once you have completed your literature review and compiled all relevant literature, it is time to screen the results. The purpose of article screening is to eliminate studies that do not meet your inclusion criteria. Two independent reviewers should screen all studies, starting with a title and abstract screen, followed by a full-text screen. A third reviewer should resolve any conflicts.

 

Title and abstract screening is the first crucial step to identify potentially relevant studies retrieved from databases or other sources based on the eligibility (inclusion and exclusion) criteria.

 

So why is title and abstract screening important?

Efficiency for study selection: Systematic reviews often identify many potentially relevant studies. Title and abstract screening allows the research team to quickly exclude irrelevant studies based on predefined eligibility criteria so that attention can be focused on more relevant studies.

• Resource savings: It could be very expensive and time consuming if you had to retrieve the full text for every potential study. Title and abstract screening prioritizes the studies for full-text review.
• Quality Control: This first step helps the research team to identify and deal with discrepancies or uncertainties with the eligibility criteria. There might be a need for more training for the team.

This key first step in the review process ensures that only studies meeting the predefined criteria are screened in full-text review.

Title and abstract screening in a systematic review should ideally be undertaken by two independent reviewers. Where there are conflicts (disagreements) in voting selection the options include a resolution between reviewers or the use of a third independent adjudicator where conflicts cannot be resolved.

This Title/Abstract stage streamlines the systematic review process by quickly narrowing down studies to those most relevant. This step reduces the time and cost associated with retrieving full texts and helps maintain focus on high-quality research. 

During the title/abstract screening, for each reference, each reviewer should read the title and abstract and make a decision:

• No: This article does not meet inclusion criteria and should not be included in our systematic review.
• Maybe: There is not enough information in the title/abstract for me to make a decision (move to full-text screen).
• Yes: This article appears to meet inclusion criteria so I would like it to move to the full-text screen.

 

Full text screening is the next step following title and abstract screening. Full text screening ensures that the included studies in the systematic review are  relevant and meet all eligibility (inclusion and exclusion) criteria.

So why is full text screening important?

Ensuring relevance: Full text screening checks whether the whole article meets the inclusion and exclusion criteria of the review. Sometimes the information provided in the title and abstract is insufficient to determine relevance or may contain inaccurate information. Full text screening therefore enables a comprehensive evaluation.

Identification of potential bias: Some studies could report additional data or outcomes in the main body of the paper that were not mentioned in the abstract. Alternatively, some outcomes that were listed in the abstract may not be reported in the full text.

Improves quality assessment: Full text screening ensures that methodological as well as outcome data are screened. This is important if methodological quality is a component of the eligibility criteria.

During full text screening the PDF/full text of the potential study is read and assessed to see if the study meets all eligibility criteria. If inclusion criteria are met the study will then be ready for data extraction. If the study is excluded then a reason must be provided for each study which can be displayed in the PRISMA figure. 

Full text screening in a systematic review should ideally be undertaken by two independent reviewers. Where there are conflicts (disagreements) in voting selection the options include a resolution between reviewers or the use of a third independent adjudicator where conflicts cannot be resolved.

During the full-text screening, for each reference, read the full-text and make a decision:

• Include: This article meets inclusion criteria and should be included in our systematic review.
• Exclude: This article does not meet inclusion criteria and should not be included in our systematic review.

Remember, all voting should be blinded, meaning your colleagues should be unable to see your votes until they have cast their own, and vice versa. 

 

We recommend that you use Rayyan or Covidence to screen your results.

Rayyan  https://www.rayyan.ai/ is a free, for some features, web and mobile app designed to help researchers manage and screen references for systematic reviews and other research projects, offering features like duplicate detection, collaboration tools, and AI-powered screening assistance. 

Covidence is a systematic reviews production tool for title/abstract screening, full-text screening, data abstraction, and quality assessment. Covidence was designed by researchers familiar with the systematic review process in order to make conducting reviews more efficient. 

The PRISMA Flow Diagram depicts the flow of information through the different phases of a systematic review. It maps out the number of records identified, included and excluded, and the reasons for exclusions. This diagram will be included in your published systematic review.