Supplementary Table 1. Assessment of risk of bias scoring table in prospective studies using the Cochrane collaboration tool

Study Random sequence generation Allocation concealment Blinding of participants and personnel Blinding of outcome assessment Incomplete outcome data Selective reporting Total Score
Fatovich 2004 [46] +1 +1 +1 0 +1 0 +4
Bottiger 2008 [41] +1 +1 +1 0 +1 +1 +5
Abu Laban 2002 [42] +1 +1 +1 0 +1 0 +4
Bottiger 2001 [40] -1 -1 -1 0 +1 +1 -1
Bozeman 2006 [45] -1 -1 -1 0 +1 +1 -1
Stadlbauer 2006 [43] 0 0 +1 0 0 +1 +2

Supplementary Table 2. Assessment of risk of bias scoring table in retrospective studies using the Newcastle-Ottawa quality assessment form for cohort studies

Selection Comparability Outcome Quality
Study Representative exposed cohort Selection of the non-exposed cohort Ascertainment of exposure Outcome of interest was not present at start of study Comparability of cohorts based on design & analysis Assess-ment of outcome Adequate follow up
Van Campen 1994 [32] Selected group * No description * Does not control for age or gender but controls for rest of variables, including comorbidities * * Fair
Schreiber 2002 [39] Selected group * No description * Does not control for age or gender; other variables are fairly similar * * Fair
Ruiz-Bailen 2001[33] Selected group * No description * Does not control for age or gender but controls for rest of variables, including comorbidities * * Fair
Lederer 2001[34] Selected group * No description * Slight differences in age and gender distribution * * Fair
Kurkciyan 2003 [38] Selected group * No description * Slight differences in age and gender distribution * * Fair
Renard 2011 [35] Selected group * No description * Baseline groups not similar.Propensity score used for statistical analysis * * Fair
Janata 2003 [36] Selected group * No description * Difference in age. Other variables were similar among the cohorts * * Fair
Kurkciyan et al. 2000 [37] Selected group * No description * Similar age and gender distribution in both cohorts * * Fair