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 (Quickx 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.

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