External validity and Bias

Study	Study design	Q11: Sample asked to participate representative of the population	Q12: Sample agreed to participate representative of the population	Q13: Staff participating representative of the patient’s environment	Q16: Data dredging results stated clearly	Q17: Analysis adjusted for length of follow up	Q18: Appropriate statistics	Q19: Reliable compliance	Q20: Accurate outcome measures
Maron et al [29]	Cross sectional	Yes	Yes	U	Yes	No	Yes	Yes	Yes
Corrado et al [30]	Cohort	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Fuller et al [31]	Cohort	Yes	Yes	Yes	Yes	U	U	Yes	U
Pelliccia et al [32]	Cross sectional	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes
Basso et al [33]	Cross sectional	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes
Baggish et al [34]	Cross sectional	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes
Hevia et al [35]	Cross sectional	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes
Magalski et al [36]	Cohort	Yes	Yes	Yes	Yes	U	Yes	Yes	Yes
Bessem et al [37]	Cross sectional	Yes	Yes	Yes	Yes	Yes	U	Yes	Yes
Sofi et al [38]	Cross sectional	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Tanaka et al [39]	Cross sectional	U	Yes	U	No	U	Yes	U	Yes
Marek et al [40]	Cohort study	Yes	Yes	Yes	Yes	U	Yes	Yes	Yes
Steinvil et al [41]	Cohort study	U	U	U	U	U	No	No	No
Wilson et al [42]	Cross sectional	Yes	Yes	Yes	Yes	U	Yes	Yes	Yes
Pelliccia et al [43]	Cross sectional	Yes	Yes	Yes	No	U	Yes	Yes	Yes
Le et al [44]	Cross sectional	Yes	Yes	Yes	Yes	U	Yes	Yes	Yes