12.8 It has been hypothesized that treatment (after casting) of a plastic used in optic lenses will improve wear. Four different treatments are to be tested. To determine whether any differences in mean wear exist among treatments, 28 castings from a single formulation of the plastic were made, and seven castings were randomly assigned to each treatment.Wear was determined by measuring the increase in “haze” after 200 cycles of abrasion

(with better wear indicated by small increases). The data are listed in table below:

a Is there evidence of a difference in mean wear among the four treatments? Use .
b Estimate the mean difference in haze increase between treatments B and C, using a 99% confidence interval. [Hint: Use the twosample t-statistic.]
c Find a 90% confidence interval for the mean wear for lenses receiving treatment A. [Hint:
Use the one-sample t-statistic.]

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Treatment A B D 9.16 11.95 11.47 11.35 13.29 15.15 9.54 8.73 12.07 14.75 11.26 10.00 11.97 14.79 13.66 9.75 13.31 15.48 11.11 11.71 12.32 13.47 15.05 12.45 11.78 13.06 14.86 12.38