Table 4.

Methodological quality appraisal using a modified Critical Appraisal Skills Programme (CASP) checklist

Item	Araszkiewicz et al. (2015)	Baker et al. (2007)	Hamdy et al. (2001)	Parkhouse et al. (1988)	Shapiro et al. (1998)	Stevens et al. (1992)	Veves et al. (1998)
1. Did the study address a clearly focused issue?	Π	Π	Π	Π	Π	Π	Π
2. Was the cohort recruited in an acceptable way?	Π	Π	Π	?	?	?	Π
3. Was the exposure accurately measured to minimise bias?	Π	Π	Π	Π	Π	Π	Π
4. Was the outcome accurately measured to minimise bias?	Π	Π	Π	Π	Π	Π	Π
5. Have the authors addressed confounding factors in the study design and/or analysis?	Π	Π	Π	?	Π	?	?
6. Are the results of the study clearly presented?	Π	Π	Π	?	Π	?	Π
7. Are the results precise?	Π	Π	Π	Π	Π	Π	Π
8. Do the results reflect a validated model?	Π	Π	Π	Π	Π	Π	Π

Π: yes; ?: not sure; Ο: no