Table 6.

Risk of bias grading in observational cohort studies following the RoB-Nobs tool

Study	D1	D2	D3	D4	D5	D6	D7	overall
Kiefte- de Jong 2013	Moderate	Serious	Low	Serious	Moderate	Low	Low	Serious
Van Gijssel 2016	Moderate	Serious	Low	Serious	Moderate	Low	Low	Serious
Routtinen 2010	Serious	Serious	Low	Serious	Moderate	Low	Moderate	Serious

ROB, risk of bias.

D1 Bias due to confounding.

D2 Bias in selection the participants into the study.

D3 Bias in classification of exposures.

D4 Bias due to departures from intended exposures.

D5 Bias due to missing data.

D6 Bias in measurement of outcomes.

D7 Bias in selection of reported result.