Question

Nine experts rated two bands of Brazilian coffee in a taste-testing experiment. A rating on a 7-point scale (1 = extremely unpleasing, 7 = extremely pleasing) is given for each of four important characteristics. The mean of the sample difference is -1.556 and the standard deviation of the sample difference is 1.424.

a. At the 5% significance level, is there evidence of a difference in the mean ratings between the two brands?

b. What assumption is necessary about the population distribution in order to perform this test?

c. Construct and interpret a 95% confidence interval estimate of the difference in the mean ratings between the two brands.

Answer 1

a)

as test staistic is in critical region we reject null hypothesis. we have sufficient evidence to conclude that there is  difference in the mean ratings between the two brands

b)

assumption required are: 1) the difference in values should be normally distributed

2) the sample should be random.

c)

for 95% CI; and 8 degree of freedom, value of t=					2.3060
margin of error E=t*std error                            =					1.095
lower confidence bound=sample mean-margin of error =					-2.65
Upper confidence bound=sample mean+margin of error=					-0.46