Table 2.
The expected mean difference (Δ̃2) between two independent groups A and B of the observed/imputed values at 2-years, the expected variance of the group difference (V(D̃2)), and the probability that a two-group test of H0: Δ2 = 0 would be nominally statistically significant at the 0.05 level one-sided, for given means of the 1 and 2-year values, assuming σ2 = 20 at each time in both groups, with a sample size of n = 200 per group, 30% of which are missing completely at random at 2-years and are replaced by the values at 1-year. Cases 2 and 7 also provide the type I error probability and power with no missing data.
| Case | μa2 | mub2 | Δ2 | μa1 | μb1 | Δ1 | Δ̃2 | V(D̃2) | Pr(significant) |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 0 | 1 | 2 | −1 | −0.3 | 0.20105 | 0.01034 |
| 2 | 1 | 1 | 0 | 1 | 1 | 0 | 0.0 | 0.20000 | 0.050 |
| 3 | 1 | 1 | 0 | 1 | 0 | 1 | 0.3 | 0.20105 | 0.165 |
| 4 | 1 | 1 | 0 | 1 | −1 | 2 | 0.6 | 0.20420 | 0.376 |
| 5 | 1 | 0 | 1 | 1 | 2 | −1 | 0.4 | 0.20420 | 0.224 |
| 6 | 1 | 0 | 1 | 1 | 1 | 0 | 0.7 | 0.20105 | 0.467 |
| 7 | 1 | 0 | 1 | 1 | 0 | 1 | 1.0 | 0.20000 | 0.723 |
| 8 | 1 | 0 | 1 | 1 | −1 | 2 | 1.3 | 0.20105 | 0.896 |