In the manufacture of soft contact lenses, the actual strength (power) of the lens needs...

In the manufacture of soft contact lenses, the actual strength (power) of the lens needs to be very close to the target value for the lenses to properly fit the customer’s needs. In the paper, ‘‘An ANOM-type test for variances from normal populations,’’ Technometrics (1997), 39: 274 –283, a comparison of several suppliers is made relative to the consistency of the power of the lenses. The following table contains the deviations from the target power of lenses produced using materials from three different suppliers:

a. Using the appropriate tests and plots given here, assess whether the data meet the necessary conditions to use an AOV to determine whether there is a significant difference in the mean deviations for the three suppliers.

b. Conduct an AOV with α =.05 and compare your results with the conclusions from (a).

c. Apply the Kruskal–Wallis test to evaluate the research hypothesis that the three suppliers have different distributions of deviations.

d. Suppose that a difference in mean deviation of 20 units would have commercial consequences for the manufacture of the lenses. Does there appear to be a practical difference in the three suppliers?