Table 2

Quality assessment of included studies

Cochrane Risk of Bias Tool (for RCTs)
Type of biasSelectionPerformanceDetectionAttritionReportingOther biases
Author YearRandom sequence generationAllocation concealmentBlinding of participants and personnelBlinding of outcome assessmentIncomplete outcome dataSelective reporting
Leader et al, 199222LowLowHigh*LowLowUnclearNone
Robinson et al, 200723LowLowHigh*High†High‡High§None
Tiplady et al, 201324LowLowHigh*High†LowUnclearHigh¶
Evidence Project Study Risk of Bias Tool (for non-RCTs)
Author YearStudy design includesComparison groups equivalent at baseline onRandom assignment (group or individual) to the interventionParticipants randomly selected for assessmentControl for potential confoundersFollow-up rate ≥75%
Preintervention and postintervention dataControl or comparison groupCohortSocio
Outcome measures
Anderson et al, 199621NoYesYesYesYesNoNoNoYes
  • *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.