=+Operation by the Application of Statistical Techniques” (Intl. J. Sci. Engr. Research, Vol. 3, Issue 5, May 2012) investigated the production process of a particular bath faucet manufactured in India. The article reported the threaded stem diameter (target value being 13 mm) of each faucet in 25 samples of size 4 as shown here:

Subgroup x1 x2 x3 x4 1 13.02 12.95 12.92 12.99 2 13.02 13.10 12.96 12.96 3 13.04 13.08 13.05 13.10 4 13.04 12.96 12.96 12.97 5 12.96 12.97 12.90 13.05 6 12.90 12.88 13.00 13.05 7 12.97 12.96 12.96 12.99 8 13.04 13.02 13.05 12.97 9 13.05 13.10 12.98 12.96 10 12.96 13.00 12.96 12.99 11 12.90 13.05 12.98 12.88 12 12.96 12.98 12.97 13.02