Problem 4-13

Johnson Filtration, Inc., provides maintenance service for water filtration systems throughout southern Florida. Customers contact Johnson with requests for maintenance service on their water filtration systems. To estimate the service time and the service cost, Johnson's managers want to predict the repair time necessary for each maintenance request. Hence, repair time in hours is the dependent variable. Repair time is believed to be related to three factors; the number of months since the last maintenance service, the type of repair problem (mechanical or electrical), and the repairperson who performs the repair (Donna Newton or Bob Jones). Data for a sample of 10 service calls are reported in the following table.

Repair Time in Hours	Months Since Last Service	Type of Repair	Repairperson
2.9	2	Electrical	Donna Newton
3.0	6	Mechanical	Donna Newton
4.8	8	Electrical	Bob Jones
1.8	3	Mechanical	Donna Newton
2.9	2	Electrical	Donna Newton
4.9	7	Electrical	Bob Jones
4.2	9	Mechanical	Bob Jones
4.8	8	Mechanical	Bob Jones
4.4	4	Electrical	Bob Jones
4.5	6

(d)	Create a new dummy variable that is equal to 0 if the repairperson is Bob Jones and 1 if the repairperson is Donna Newton. Develop the multiple regression equation in Excel to predict repair time, given the number of months since the last maintenance service and the repairperson.
	Letx1represent the number of months since the last maintenance service.
Letx2represent the repairperson.
	If required, round your answers to four decimal places. For subtractive or negative numbers use a minus sign even if there is a + sign before the blank. (Example: -300)
	=+x1+x2
	What are the interpretations of the estimated regression parameters?
	The input in the box below will not be graded, but may be reviewed and considered by your instructor.
	What is the coefficient of determination?
	If required, round your answers to four decimal places.
	Interpret the coefficient of determination.
	The input in the box below will not be graded, but may be reviewed and considered by your instructor.
(e)	Develop the multiple regression equation to predict repair time given the number of months since the last maintenance service, the type of repair, and the repairperson.
Letx1represent the number of months since the last maintenance service.
Letx2represent the type of repair.
Letx3represent the repairperson.
If required, round your answers to four decimal places. For subtractive or negative numbers use a minus sign even if there is a + sign before the blank. (Example: -300).
	=+x1+x2+x3
	What are the interpretations of the estimated regression parameters?
	The input in the box below will not be graded, but may be reviewed and considered by your instructor.
	What is the coefficient of determination?
	If required, round your answers to four decimal places.