Table 1 Study design options of the “Healthful & Tasty: Sure!” workplace trial
Experimental study design | Alternative quasi-experimental study design | |
|---|---|---|
Design | Cluster randomized controlled trial | Cluster nonrandomized single arm trial with calibration arm |
Blinding | No | No |
Pair-wise matching | Yes | No |
Sample size estimation (power calculation) | Assumptions: baseline mean 24-h urine sodium excretion of 180 mmol [16, 17, 42], standard deviation of 65, intra-cluster correlation coefficient of 0.05, 16 clusters and drop-out rate of 25%. Objective: detect between-group difference of at least 15% (i.e. 27 mmol) at trial end with alpha 0.05 and 80% power. | Assumptions: baseline mean 24-h urine sodium excretion of 180 mmol [16, 17, 42], standard deviation of 65, intra-cluster correlation coefficient of 0.05, and drop-out rate of 10%. Objective: detect sodium intake reduction by 15% (i.e. 27 mmol) until trial end with alpha 0.05 and 80% power. |
Numbers required to measure effectiveness | Number of clusters (participants, before 25% drop-out) 8 intervention clusters (N = 395, 50 per cluster) 8 control clusters (N = 395, 50 per cluster) | Number of clusters (participants, before 10% drop-out) 7 intervention clusters (N = 112, 16+ per cluster) |