Sample size
Group sample sizes of 43 and 43 achieve 90% power to reject the null hypothesis of equal means when the population mean difference of preoperative nursing care time is 5 min and - with a standard deviation for both groups of 7 min and with a significance level (alpha) of 0.050. Assuming a 20% potential dropout rate, the final sample size was increased to 120 subjects, with 60 subjects in each intervention group.