In response to a complaint that a particular tax assessor (A) was biased, an experiment was conducted

Question:

In response to a complaint that a particular tax assessor (A) was biased, an experiment was conducted to compare the assessor named in the complaint with another tax assessor (B) from the same office. Eight properties were selected, and each was assessed by both assessors. The assessments (in thousands of dollars) are shown in the table.

Use the MINITAB printout to answer the questions that follow.
Paired T-Test and CI: Assessor A, Assessor B
Paired T for Assessor A - Assessor B

95% lower bound for mean difference: 0.489
T-Test of mean difference = 0 (vs > 0):
T-Value = 2.82 P-value = 0.013
a. Do the data provide sufficient evidence to indicate that assessor A tends to give higher assessments than assessor B?
b. Estimate the difference in mean assessments for the two assessors.
c. What assumptions must you make in order for the inferences in parts a and b to be valid?
d. Suppose that assessor A had been compared with a more stable standard-say, the average of the assessments given by four assessors selected from the tax office. Thus, each property would be assessed by A and also by each of the four other assessors and (xA -) would be calculated. If the test in part a is valid, can you use the paired-difference t-test to test the hypothesis that the bias, the mean difference between A's assessments and the mean of the assessments of the four assessors, is equal to 0? Explain.