4. A crossover trial is planned to evaluate the impact of an educational interve

Question

4.  A crossover trial is planned to evaluate the impact of an educational intervention program to reduce alcohol consumption in patients determined to be at risk for alcohol problems. The plan is to measure alcohol consumption (the number of drinks on a typical drinking day) before the intervention and then again after participants complete the educational intervention program. How many participants would be required to ensure that a 95% confidence interval for the mean difference in the number of drinks is within 2 drinks of the true mean difference? Assume that the standard deviation of the difference in the mean number of drinks is 6.7 drinks and that 20% of the participants will drop out over the course of follow up.

Explanation / Answer

here margin of error E=2

and std deviation =6.7

for 95% CI, z=1.96

drop out rate =0.2

hence sample size =(1/(!-0.2))*(z*std deviation/margin of error)2 =~54

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