Table 3
Statistical Analysis of a Cluster-randomized Trial
| Statistical Test | Test Statistic (df) | pValue | Effect Size | 95% CI |
| Ignoring clustering in the analysis (incorrect approach): | ||||
| Chi-square test | χ2=6.95 (1 df) | 0.008 | PD=7% | 2%–12% |
| OR=1.5 | 1.1–2.0 | |||
| Cluster-level analyses: | ||||
| Two-sample t test | t=1.84 (32 df) | 0.074 | MD=8% | -1%–17% |
| Weighted t test | t=2.09 (32 df) | 0.044 | WMD=7% | 0%–14% |
| Individual-level analyses that account for clustering: | ||||
| Random effects model | t=2.00 (1,097 df) | 0.046 | OR=1.5 | 1.0–2.3 |
| Generalized estimating equations | z=2.06 | 0.040 | OR=1.5 | 1.0–2.1 |
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Abbreviations: PD indicates proportion difference; MD, mean difference; WMD, weighted mean difference; OR, odds ratio; CI, confidence interval; df, degree of freedom.
