Quality assessment of included studies
| Cochrane Risk of Bias Tool (for RCTs) | |||||||
| Type of bias | Selection | Performance | Detection | Attrition | Reporting | Other biases | |
| Author Year | Random sequence generation | Allocation concealment | Blinding of participants and personnel | Blinding of outcome assessment | Incomplete outcome data | Selective reporting | |
| Leader et al, 199222 | Low | Low | High* | Low | Low | Unclear | None |
| Robinson et al, 200723 | Low | Low | High* | High† | High‡ | High§ | None |
| Tiplady et al, 201324 | Low | Low | High* | High† | Low | Unclear | High¶ |
| Evidence Project Study Risk of Bias Tool (for non-RCTs) | |||||||||
| Author Year | Study design includes | Comparison groups equivalent at baseline on | Random assignment (group or individual) to the intervention | Participants randomly selected for assessment | Control for potential confounders | Follow-up rate ≥75% | |||
| Preintervention and postintervention data | Control or comparison group | Cohort | Socio demographics | Outcome measures | |||||
| Anderson et al, 199621 | No | Yes | Yes | Yes | Yes | No | No | No | Yes |
*Blinding of participants and personnel not possible, based on the intervention.
†Blinding of outcome assessment not possible for self-reported pregnancy (via positive pregnancy test).
‡Unexplained high dropout rate (35%): 191 non-responders in the OPK group and 144 in the control group.
§Unreported outcome (live birth). Study reported results from two menstrual cycles, instead of from the prespecified three cycles (‘Although women were recruited to the study for three cycles, insufficient evaluable data were provided for the third cycle of the study, and therefore data were analysed for the first two complete cycles following confirmation that the participants were not pregnant at baseline. The reason for the limited third-cycle data was thought to be related to confusion on the part of the participants regarding returning data at the end of cycle 3.’).
¶A second (biased, ratio 2:1) cohort was recruited into the OPK group to increase the power of the data for the outcome stress, because of higher pregnancy rates in the OPK group.
OPK, ovulation predictor kit; RCTs, randomised controlled trials.