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Sample size calculations

EH Esmat Heydari
TD Tahereh Dehdari
MS Mahnaz Solhi
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The formula “n = (Z 1-α/2+Z1-β)2. (S12+S22)/d2” was used to calculate the sample size. Input data to estimate the needed sample size came from the findings of a pilot study that had been conducted by the present trial researchers. Given that the perceived severity was recognized as a main predictor of adopting sun-safe practices in seafarers [5], standard deviations of the variable of both intervention and control groups at 1 month (15.67 and 21.35) were used. A total of 136 seafarers (n = 68 per group) provided sufficient statistical power (> 80%) with an alpha of 0.05 (2-sided) to detect the difference of 10 scores in the change in the skin cancer preventive behaviors at 1 month from the baseline compared with the control group over the 1-month study interval, allowing for up to 25% loss to follow up.

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