Six Sigma Case Studies with Minitab®

161

10

Multivariate Analysis to Reduce Patient

Waiting Time at a Medical Center

This case study is about a Six Sigma project implemented by the quality

department at Quickx Medical Center. The administration aims to reduce

the patient waiting time before treatment.

Sections 10.1 and 10.2 give brief descriptions of the dene phase and the

measure phase, respectively. Section 10.3 illustrates the analyze phase with

detailed instructions for using Minitab

®

. Finally, Sections 10.4 and 10.5 give

brief descriptions of the improve phase and the control phase, respectively.

10.1 Define Phase

The quality department has been asked by the administration to reduce the

patient waiting time. To this end, the quality department brainstorms and

identies the following two factors that they believe might have an effect on

the patient waiting time:

• Location (Quickx has two locations: Copley and Kenmore.)

• Service type (Quickx serves in three areas: internal medicine, pedi-

atrics, dermatology.)

The problem statement is “to reduce the patient waiting time”.

10.2 Measure Phase

For a preliminary process analysis, the quality department collects data

(waiting time in minutes) for a random sample of four patients for each com-

bination of location and service type, as shown in Table10.1.

The qualitative variables (e.g., Copley, pediatrics, etc.) are then coded as

shown in Table10.2 so that it is easier to enter the data in Minitab

®

.

162 Six Sigma Case Studies with Minitab

®

In Table10.2, the levels of Location are coded as 1 (for Copley) and 2 (for

Kenmore). The levels of Service Type are coded as 1 (for Internal Medicine),

2 (for Pediatrics), and 3 (for Dermatology).

Figure10.1 partially shows the waiting times of the patients as entered in

the Minitab

®

worksheet. Refer to the CHAPTER_10_1.MTW worksheet for

FIGURE 10.1

Sample of patient waiting times.

TABLE10.1

Sample Data

Internal Medicine Pediatrics Dermatology

Copley 35, 24, 42, 21 12, 54, 10, 9 25, 32, 34, 45

Kenmore 42, 35, 21, 34 19, 18, 17, 23 10, 9, 4, 11

TABLE10.2

Revised Sample Data (Coded Levels of Factors)

1 2 3

1 35, 24, 42, 21 12, 54, 10, 9 25, 32, 34, 45

2 42, 35, 21, 34 19, 18, 17, 23 10, 9, 4, 11

163Multivariate Analysis to Reduce Patient Waiting Time at a Medical Center

the complete set of data (the worksheet is available at the publisher’s website;

the data from the worksheet are also provided in the Appendix).

10.3 Analyze Phase

The quality team plots multivariate charts to verify whether waiting time

indeed depends on location and service type, and also whether there is any

interaction between location and service type.

Open the CHAPTER_10_1.MTW worksheet, and click on “Multi-Vari

Chart” as shown in Figure10.2. As a result, the dialog box shown in Figure10.3

opens. Using the “Select” button, select “Waiting Time” for “Response”,

“Location” for “Factor 1”, and “Service Type” for “Factor 2”. Then, click on

“Options”, and the dialog box shown in Figure10.4 opens. Check the boxes

for “Connect Means for Factor 1” and “Connect Means for Factor 2” if they

FIGURE 10.2

Selection of “Multi-Vari Chart”.