Biostatistics
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1. The mean body mass index (BMI) for boys age 12 is 23.6. An investigator wants to test if the BMI is higher in 12yearold boys living in New York City. How many boys are needed to ensure that a twosided test of hypothesis has 80% power to detect a difference in BMI of 2 units? Assume that the standard deviation in BMI is 5.7.
=
Alpha = ________
Z1α/2= ________
Z1β = ________
ES = ________
n= ________
2. An investigator wants to estimate caffeine consumption in high school students. How many students would be required to estimate the proportion of students who consume coffee? Suppose we want the estimate to be within 5% of the true proportion with 95% confidence.
Alpha = ________
Z= ________
p= ________
Effect Size = ________
n= ________
3. 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.
Z= ________
s= ________
Effect Size = ________
n= ________
Sep 17th, 2013
Given a=0.2 Z(0.1)=1.28 (check standard normal table)
power=0.8, Z(0.2)=0.84(check standard normal table)
s=5.7, E=2
So n={(Z(1a/2) + Z(1power))/E}^2*s^2
=[(1.28+0.84)/2]^2*5.7^2
=36.50576
So take n=37
2 a. Given a=0.05, Z(0.025)=1.96 (check standard normal table)
So n=(Z*s/E)^2
=(1.96*68/15)^2
= 78.94915
Take n=79
3. Given a=0.05, Z(0.025)=1.96 (check standard normal table)
So n=(Z*s/E)^2
=(1.96*6.7 /2)^2
=43.11236
Take n=44
power=0.8, Z(0.2)=0.84(check standard normal table)
s=5.7, E=2
So n={(Z(1a/2) + Z(1power))/E}^2*s^2
=[(1.28+0.84)/2]^2*5.7^2
=36.50576
So take n=37
2 a. Given a=0.05, Z(0.025)=1.96 (check standard normal table)
So n=(Z*s/E)^2
=(1.96*68/15)^2
= 78.94915
Take n=79
3. Given a=0.05, Z(0.025)=1.96 (check standard normal table)
So n=(Z*s/E)^2
=(1.96*6.7 /2)^2
=43.11236
Take n=44
Sep 17th, 2013
Trusted solution. Please aprove
Sep 17th, 2013
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Sep 17th, 2013
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Sep 17th, 2013
Oct 22nd, 2016
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