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Table 1 Study design options of the “Healthful & Tasty: Sure!” workplace trial

From: Study design and baseline characteristics of a combined educational and environmental intervention trial to lower sodium intake in Swiss employees

  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)