2.3. Data extraction

Data were extracted by one reviewer (CE) with the following information: author, year of publication, country, cognitive domain measured, corresponding cognitive test or battery, maximum interval between baseline and follow‐up measurement, study sample size, age range of participants, patient group (RRMS, PPMS, and SPMS), MS duration (mean, median, range), baseline EDSS, how a change in cognitive function was measured, study findings related to cognitive function, and the intervention/s used (if applicable). Although the information on many cognitive domains and tests was extracted, only studies with SDMT mean score and standard deviation at baseline and follow‐up and sample size at baseline and follow‐up were used for the meta‐analysis. Fifteen authors were contacted through email for some missing information for the meta‐analysis but five responded. Only papers with complete data were used for the meta‐analysis. SDMT was chosen because it is sensitive to cognitive function changes and has been recommended as the best clinical practice tool for the assessment of cognitive function in PwMS (Kalb et al., 2018).

The quality and risk of bias assessment of the included studies was assessed by 2 reviewers (CE and AZ) independently using the Newcastle–Ottawa Scale (NOS). Stars were assigned to the included publications based on three criteria: selection of cases/controls or cohorts, comparability of cases/controls or cohorts, and outcome assessment with a maximum of four, two and three stars respectively. For each publication, total stars ranging from 0 to 3, 4 to 6, and 7 to 9 were considered as low (high risk of bias), moderate (moderate risk of bias), and high quality (low risk of bias), respectively.