The deflection temperature under load for two different types of plastic pipe is being investigated. Two random samples of 15 pipe specimens are tested, and the deflection temperatures observed are as follows (in oF): Type 1: 206, 188, 205, 187, 194, 193, 207, 185, 189, 213, 192, 210, 194, 178, 205. Type 2: 177, 197, 206, 201, 180, 176, 185, 200, 197, 192, 198, 188, 189, 203, 192.
(a) Construct box plots and normal probability plots for the two samples. Do these plots provide support of the assumptions of normality and equal variances? Write a practical interpretation for these plots.
(b) Do the data support the claim that the deflection temperature under load for type 2 pipe exceeds that of type 1? In reaching your conclusions, use a = 0.05.
(c) Calculate a P-value for the test in part (b).
(d) Suppose that if the mean deflection temperature for type 2 pipe exceeds that of type 1 by as much as 5oF, it is important to detect this difference with probability at least 0.90. Is the choice of n1 = n2 = 15 in part (a) of this problem adequate?