TABLE 4.

Risk of bias assessment of the eight included studies according to the QUIPS tool

Source	Study participation	Study attrition	Exposure measurement	Outcome measurement	Confounding	Statistical analyses and presentation	Overall risk of bias
Kongsted et al. (2008)
Maujean et al. (2017)
Pedler et al. (2016)
Ravn et al. (2019)
Ravn, Sterling, et al. (2018)
Ramchand et al. (2008)
Andersen et al. (2016)
Åsenlöf et al. (2013)

Note: Green, yellow and red indicate low, moderate and high risk of bias respectively.