Double- versus single-balloon catheters for labour induction and cervical ripening: a meta-analysis

Table 2 Risk of bias and corresponding quality

Study	Risk of bias for the included studies							Quality
Study	Random sequence generation (selection bias)	Allocation concealment (selection bias)	Blinding of participants and personnel (performance bias)^x	Blinding of outcome assessment (detection bias)	Incomplete outcome data (attrition bias)	Selective reporting (reporting bias)^y	Other bias	Quality
Ahmed 2016	L	L	U	U	L	L	L	H
Haugland 2012	L	U	L	L	L	L	U	M
Hoppe 2015^A	L	L	H	H	L	L	L	M
Pennell 2009	L	L	H	L	L	L	L	H
Rab 2014	L	U	U	L	L	L	L	M
Salim 2011^A	L	L	H	U	L	L	L	H
Solt 2009^B	L	L	H	L	L	H	U	M

Other bias: trials sponsored by drug companies or trials in which baseline characteristics were not similar between different intervention groups
L: Low risk or low quality. For the risk of bias, L means appropriate methods were adequately described
H: High risk or high quality. For the risk of bias, H means high risk was found (unable to avoid bias)
U: Unclear risk, no description
M: Moderate quality
A: Hoppe et al. [17] and Salim et al. [20] reported a few lost follow-ups and did not perform intention-to-treat (ITT) analyses. Fortunately, they were balanced in numbers with similar reasons across intervention groups and had little influence on the following analysis. Therefore, we assessed the attrition bias as low
B: Solt et al. [21] only described a single-blind method. Considering the nature of the study, we evaluated performance bias as H, while detection bias was evaluated as L. Additionally, they selectively reported outcomes for the nulliparous group, and we could not obtain supplemental data for the multiparous group by contacting the author
x: Blinding of participants and personnel, though graded, was excluded from the quality assessment because it was impractical for these trials
y: Some studies did not offer their protocols; therefore, it is difficult hard to determine whether the outcomes were not measured or not reported. Unless selective reporting was obvious, we evaluated this situation as being low risk

ISSN: 1471-2393