What is the estimated 95% confidence interval (CI) of the average difference in blood vitamin D levels between short sleeve shirt and tank top attire amongst US landscapers in ng/mL?

Please note the following: 1) in practice, you as the analyst decide how to calculate the difference in vitamin D levels between time points for a given study participant, and subsequently interpret the aggregated results appropriately in the context of the data, though for the purposes of this exercise the difference is assigned for you as follows.Define the difference as the second minus the first time points, which is common practice, since the plus or minus sign of the resulting difference reflects any change over sequential time; 2) you might calculate a CI that is different from any of the multiple choice options listed below due to rounding differences, therefore select the closest match; 3) ensure you use either the large or small sample CI formula as appropriate; and 4) you may copy and paste the data into Excel to facilitate analysis.

Select one:

a. -15.52 to -6.16 ng/mL

b. -15.66 to -4.76 ng/mL

c. -15.18 to -5.86 ng/mL

d. -13.50 to -5.35 ng/mL

Time Point I , Shirts Time Paint 2, Tank Tops Subjact VimmlnD Inggle Vitamin D lngle Iii-i'- 31932 m 50.332 35.154 n n n n n 51:42 33.7?1 11 53.36? 33321