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Who can help assist with two questions? 

The mean body mass index (BMI) for boys of age 12 years is 23.6. An investigator wants to test if the BMI is higher in 12 years old boys living in New York City. How many boys are needed to ensure that a two sided 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.

Consider a study designed to assess the association between obesity, defined as a body mass index (BMI) of 30 and more and the incidence of cardiovascular disease. Data are collected in a cohort study in which participants ages 35 and 65 who were free of cardiovascular disease (CVD) are enrolled and followed over 10 years. Each participant’s BMI is assessed at baseline and particxipants are followed for 10 years for incident cardiovascular disease. A summary of the data are given below:

Incident CVD No CVD Total

Obese 46 254 300

Not obese 60 640 700

Total 106 894 1000

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