SOLUTION: 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.

Question 1088741: 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 requires 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.
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
95% CI is mean +/- 1.96 * s/ sqrt(n), assuming n is large enough. If not, will need to use t.
the half interval is width 2.
therefore, +/-1.96 *6.7/(sqrt(n)=2
13.132/sqrt(n)=2
square both sides
172.45=4n
n=43.11 or 44.
This requires a t, since the t-value is 2.017
will still use 44 as it was rounded up.
2.017*6.7/sqrt (44)=2.037.
try n=45
t=2.015, interval is 2.012
try n=47
t=2.013, interval is 1.97
try n=46
2.014; interval is 1.99
46.

RELATED QUESTIONS
A crossover trial is planned to evaluate the impact of an educational intervention... (answered by stanbon)

A study is conducted to assess the impact of caffeine consumption, smoking, alcohol... (answered by SadieKhan)

A study is conducted to assess the impact of caffeine consumption, smoking, alcohol... (answered by stanbon)

A small software company publishes computer games, educational software, and utility... (answered by ikleyn)

A crossover trial is conducted to compare an experimental medication for migraine... (answered by rjernej1)

If the price of petrol is increased by 30%how much percent a car owner must reduce his... (answered by ikleyn)

how much water must be added to 4 gallons of an 8% alcohol beer to reduce the alcohol... (answered by josgarithmetic)

The price of milk is increased by 20%.Find by how much percent a housewife should reduce... (answered by josmiceli)

how much water must be added to 50 gallons of a 40% alcohol solution to reduce the... (answered by ptaylor)