Question

The average BMI of the 241 patients who contracted an SSI in the Seasonal Effect data set is approximately 27.9 with a sample standard deviation of approximately 6.53. Use this information to answer questions 4-6.

2. Create and interpret a 95% confidence interval for the mean BMI of patients contracting an SSI. Show your work. (15%)

Answer 1

Sol:

degrees of freedom=df=n-1=241-240

sample size=n-=241

sample mean =xbar=27.9

sample stddevs=6.53

alpha=0.05

alpha/2=0.05/2=0.025

critical t value for 0.025 and 240 df is =T.INV(0.025;240)=1.969897635

95% confidence interval for the mean BMI of patients contracting an SSI

=xbar-tcrit*s/sqrt(n),xbar+tcrit*s/sqrt(n)

=27.9-1.969897635*6.53/sqrt(241),27.9+1.969897635*6.53/sqrt(241)

= 27.07139,28.72861

lower limit=27.071

upper limit=28.729

intrepretation:

we are 95% confident that the true population mean  BMI of patients contracting an SSI lies in between

27.071 and 28.729