Table 3.
Risk-of-bias summary: review authors’ judgements of each risk-of-bias item for each included studya
| Study | Case (1) | Control (2) | Selection bias (3) | Defined exposure (4) | Determination exposure (5) | Confounding (6) | Overallb |
|---|---|---|---|---|---|---|---|
| Ficek et al. [28] 2013 | + | + | ? | + | ? | + | ? |
| Ficek et al. [29] 2014 | + | + | ? | + | ? | + | ? |
| Khoschnau et al. [30] 2008 | + | ? | + | + | + | − | − |
| Khoury et al. [31] 2015 | + | + | ? | + | ? | − | − |
| Malila et al. [32] 2011 | + | + | ? | + | ? | − | − |
| Mannion et al. [33] 2014 | + | + | ? | + | ? | − | − |
| O’Connell et al. [34] 2015 | + | ? | ? | + | + | − | − |
| Posthumus et al. [35] 2009 | + | + | ? | + | ? | − | − |
| Posthumus et al. [36] 2009 | + | + | ? | + | ? | + | ? |
| Posthumus et al. [37] 2010 | + | + | ? | + | ? | − | − |
| Posthumus et al. [38] 2012 | + | + | ? | + | ? | + | ? |
| Rahim et al. [39] 2014 | + | ? | ? | + | ? | - | − |
| Raleigh et al. [40] 2013 | + | + | ? | + | ? | + | ? |
| Stępień-Słodkowska et al. [41] 2013 | + | + | ? | + | ? | ? | ? |
| Stępień-Słodkowska et al. [42] 2015 | + | + | ? | + | ? | ? | ? |
| Stępień-Słodkowska et al. [43] 2015 | + | + | ? | + | ? | ? | ? |
aNumbers 1–6 in the column headings correspond to the questions listed in Table 1; − indicates the risk of bias question was answered ‘no’, + indicates the risk of bias question was answered ‘yes’, ? indicates the risk of bias question could not be answered either ‘yes’ or ‘no’ and was answered with a ‘doubtful’ or ‘unknown’
b− indicates a high risk of bias, ? indicates an unclear risk of bias