Evidence Synthesis: Screening

The screening process aids in the removable of studies that don't follow your inclusion criteria.

You'll first begin by screening the title and the abstract of each of the studies. This will help you determine if they're truly relevant to your research question. Please note that there will be items are not related.

After the initial screening, review the full text and proceed based on the inclusion and exclusion criteria.

According to Cochran: 

"Eligibility criteria do not exist in isolation, but should be specified with the synthesis of the studies they describe in mind. This will involve making plans for how to group variants of the PICO elements for synthesis. This chapter describes the processes by which the structure of the synthesis can be mapped out at the beginning of the review, and the interplay between the review question, considerations for the analysis and their operationalization in terms of eligibility criteria. Decisions about which studies to include (and exclude), and how they will be combined in the review’s synthesis, should be documented and justified in the review protocol" (McKenzie et. al).

Sources:

McKenzie JE, Brennan SE, Ryan RE, Thomson HJ, Johnston RV, Thomas J. Chapter 3: Defining the criteria for including studies and how they will be grouped for the synthesis [last updated August 2023]. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.5. Cochrane, 2024. Available from www.training.cochrane.org/handbook.

Cochran defines bias "as a systematic error, or deviation from the truth, in results" (Boutron et al 2022).

They also state: "Biases can lead to under-estimation or over-estimation of the true intervention effect and can vary in magnitude: some are small (and trivial compared with the observed effect) and some are substantial (so that an apparent finding may be due entirely to bias). A source of bias may even vary in direction across studies" (Boutron et al 2022).

Sources:

Boutron I, Page MJ, Higgins JPT, Altman DG, Lundh A, Hróbjartsson A. Chapter 7: Considering bias and conflicts of interest among the included studies [last updated August 2022]. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.5. Cochrane, 2024. Available from www.training.cochrane.org/handbook.

Tools

Cochrane Handbook for Systematic Reviews of Interventions 

• Risk of Bias 2 (RoB 2) Tool
• Chapter 7: Considering bias and conflicts of interest among the included studies

Catalog of Bias (CEBM & Oxford University)

• List of all Biases in the Catalogue