An investigator wants to design a study to estimate the difference in the mean B

Question

An investigator wants to design a study to estimate the difference in the mean BMI between boys and girls age 12 living in New York City. How many boys and girls are needed to ensure that a 95% confidence interval estimate for the difference in mean BMI between boys and girls has a margin of error not exceeding 2 units? use the estimate of the variability in BMI from the following..the mean body mass index (BMI) for boys age 12 is 23.6. An investigator wants to test if the BMI is higher in boys age 12 living in New York City. How many boys are needed to ensure that a two sided test of hypothesis has 80% power to detect an increase in BMI of 2 units? Assume that the standard deviation is BMI is 5.7.

Explanation / Answer

1)

The formula is 2*variability*(z(0.975))/error margin)^2

variability = 23.6

z(0.975) = 1.96

error margin = 2

n = 2(23.6)(1.96/2)^2 = 45.3 which conservatively rounds up to 46

So 46 boys and 46 girls are needed.

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