Table 3.
Results of risk of bias assessment
| Studies | Selection | Comparability | Exposure | Score/Stars | Overall quality | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 1a | 1b | 1 | 2 | 3 | |||
| Bank et al. [38] | * | * | * | * | * | 5 | Fair | ||||
| Becerra et al. [41] | * | * | * | * | * | 5 | Fair | ||||
| Dietz et al. [65] | * | * | * | * | * | 5 | Fair | ||||
| Drummond et al. [63] | * | * | * | 3 | Low | ||||||
| Eberle et al. [73] | * | * | * | 3 | Low | ||||||
| Edinger et al. [55] | * | * | * | * | * | * | 6 | Fair | |||
| Enax-Krumova et al. [16] | * | * | * | * | 4 | Low | |||||
| Gierthmühlen et al. [15] | * | * | * | * | * | * | 6 | Fair | |||
| Gossrau et al. [72] | * | * | * | * | * | * | 6 | Fair | |||
| Habig et al. [71] | * | * | * | * | * | 5 | Fair | ||||
| Huge et al. [47] | * | * | * | * | * | * | 6 | Fair | |||
| Huge et al. [61] | * | * | * | * | * | * | 6 | Fair | |||
| Kemler et al. [44] | * | * | * | 3 | Low | ||||||
| Knudsen et al. [54] | * | * | * | 3 | Low | ||||||
| Kolb et al. [61] | * | * | * | * | * | 5 | Fair | ||||
| König et al. [39] | * | * | * | * | 4 | Low | |||||
| König et al. [40] | * | * | * | * | 4 | Low | |||||
| Kumowski et al. [53] | * | * | * | * | * | * | 6 | Fair | |||
| Maier et al. [69] | * | * | * | * | * | 5 | Fair | ||||
| Mainka et al. [49] | * | * | * | * | 4 | Low | |||||
| Thimineur et al. [57] | * | * | * | * | 4 | Low | |||||
| Meyer-Frießem et al. [60] | * | * | * | * | * | 5 | Fair | ||||
| Munts et al. [70] | * | * | * | * | * | * | 6 | Fair | |||
| Palmer et al. [52] | * | * | * | * | * | 5 | Fair | ||||
| Raj et al. [59] | * | * | * | 3 | Low | ||||||
| Rasmussen et al. [43] | * | * | * | * | * | 5 | Fair | ||||
| Reimer et al. [14] | * | * | * | * | * | 5 | Fair | ||||
| Seifert et al. [45] | * | * | * | * | 4 | Low | |||||
| Sethna et al. [46] | * | * | * | * | * | * | 6 | Fair | |||
| Sieweke et al. [62] | * | * | * | * | * | 5 | Fair | ||||
| Terkelsen et al. [18] | * | * | * | * | * | * | * | 7 | Good | ||
| Truffyn et al. [64] | * | * | * | * | * | 5 | Fair | ||||
| Uçeyler et al. [66] | * | * | * | * | * | 5 | Fair | ||||
| van Rooijen et al. [50] | * | * | * | * | * | 5 | Fair | ||||
| van Rooijen et al. [51] | * | * | * | * | * | 5 | Fair | ||||
| Vartiainen et al. [42] | * | * | * | * | 4 | Low | |||||
| Vatine et al. [48] | * | * | * | * | 4 | Low | |||||
| Weber et al. [58] | * | * | * | * | * | 5 | Fair | ||||
| Wittayer et al. [68] | * | * | * | * | * | * | 6 | Fair | |||
| Wolanin et al. [56] | * | * | * | * | 4 | Low | |||||
Selection: (1) the case definition being adequate, (2) representativeness of the cases, 3) selection of controls, (4) definition of controls. Comparability: (1a) study controls of age, (1b) study controls for additional important factor as gender. Exposure: (1) ascertainment of exposure, (2) same method of ascertainment for cases and controls, (3) non-response rate. (*) means the study passed the assessment category