14.29 Regression for telephone holding times Refer to the previous exercise. Let x1 = 1 for the advertisement and 0 otherwise, x2 = 1 for Muzak and 0 otherwise, and x1 = x2 = 0 for classical music. Likewise, let x3 = 1 for repeating in 10-minute cycles and x3 = 0 for repeating in 5-minute cycles. The display shows results of a regression of the telephone holding times on these indicator variables.

a. Give the corresponding regression model for the population mean and show the equation for the population mean at each setting of the two factor levels. (Create a table similar to Table 14.11.)

b. State the prediction equation. Interpret the parameter estimates.

c. Find the estimated means for the six groups in the twoway cross-classification of type of recording and repeat time.

d. Find the estimated difference between the mean holding times for 10-minute repeats and 5-minute repeats, for a fixed recording type. How can you get this estimate from a coefficient of an indicator variable in the prediction equation?

e. Find a 95% confidence interval for the difference between the mean holding times for 10-minute repeats and 5-minute repeats.

Transcribed Image Text:

Regression for telephone holding times Term Constant Coef 8.867 SE Coef T-Value P-Value 1.776 4.99 0.000 x1 -5.000 2.051 -2.44 0.033 x2 x3 -7.600 2.051 -3.71 0.003 2.556 1.709 1.50 0.163