Table 3.
Parameter values and trial characteristics initially chosen for the simulation-based power calculations of the IPD meta-analysis of pregnancy trials
| Parameter | Chosen values | Interpretation and justification |
|---|---|---|
| No. of trials | 14 | Number of studies included in a previous aggregate data meta-analysis that had promised their IPD |
| Sample sizes | 50, 931, 125, 85, 235, 327, 45, 12, 39, 142, 105, 84, 15, 124 | Total sample size: taken from original trial publications (could breakdown further into the number in control and treatment groups if unequal) |
| α i | 13.30, 5.00, 9.68, 10.60, 11.50, 15.24, 14.20, 5.20, 5.00, 12.40, 13.80, 8.00, 15.70, 15.40 | Mean weight gain in the control group: used values as stated in original trial publications |
| β | −0.28 | Prognostic effect of BMI on weight gain: used estimate from a meta-regression of mean weight gain against mean baseline BMI in the control group |
| θ | −0.84 | Mean treatment effect across trials: used summary estimate from random effects meta-analysis of published estimates from the 14 trials |
| λ | Various: −0.5, − 0.4, − 0.3, − 0.2, − 0.1, −.05, − 0.025, − 0.01 | Magnitude of interaction: used range from extremely large to extremely small interaction effect |
| 43.25, 15.57, 119.26, 52.69, 16.98, 37.37, 33.89, 6.63, 12.93, 12.63, 15.22, 12.93, 13.78, 40.53 | Residual variance: used unweighted average of the variance values for treatment and control groups as stated in original trial publications | |
| 0 | Between-study variance of the prognostic effect of baseline BMI: set to zero for parsimony | |
| 1.1 | Between-study variance of overall treatment effect: used estimate from random effects meta-analysis of published estimates from the 14 trials | |
| 0 | Between-study variance of interaction effect: set to zero for parsimony | |
| Distribution of baseline BMI values | Study 1: N(34.75, 12.5) Study 2: N(30.15, 25.51) Study 3: N(37.95, 0.49) Study 4: N(33.63, 14.77) Study 7: N(24.55, 27.45) Study 8: N(35.1, 12.25) Study 10: N(23.85, 0.25) Study 12: N(25.45, 13.45) Study 13: N(23.65, 18.13) Other studies had a mean drawn from N(30, 2.5) and within-trial standard deviation set at 3.5 |
Distribution of key covariate of interest: assumed normality, with means and variances as stated in original trial publication, or if unavailable, values based on those observed from within and between other trials |