Fig 1.
Flow diagram of literature search, eligibility and inclusion process according to PRISMA statement.
Fig 2.
Risk-of-bias ratings for epidemiological studies (n = 42).
Criteria ratings served as the basis for the assignment of individual studies to one out of 3 study quality categories (1st tier, 2nd tier, 3rd tier; see S1 Fig). Black frames indicate key risk-of-bias criteria.
Fig 3.
Risk-of-bias ratings for experimental studies (n = 11).
Criteria ratings served as the basis for the assignment of individual studies to one out of 3 study quality categories (1st tier, 2nd tier, 3rd tier; see S1 Fig). Black frames indicate key risk-of-bias criteria.
Fig 4.
Overview of study quality and effects/associations found in the included studies.
Each study is represented by a numbered and colored point, indicating the study quality assessed with the risk-of-bias tool recommended by OHAT [37, 39] (1/green = 1st tier, 2/yellow = 2nd tier, 3/red = 3rd tier). Each study is allocated to an effect category (columns) according to the conclusive result stated by the authors (cf. S4–S10 Tables). Please note that Roser et al. (2016) [45] investigated both cognitive functions and behavior and was therefore considered in both lines separately.