Six Sigma Case Studies with Minitab®

185

11

Pareto Chart and Fishbone

Diagram to Minimize Recyclable

Waste Disposal in a Town

Town XYZ collects the following recyclable trash from its residents: glass,

plastic, paper, aluminum, yard waste, and iron. One of its primary aims for

next year is to encourage residents to reuse the recyclables as much as pos-

sible before disposing of them.

Section 11.1 briey describes the dene and measure phases. Section 11.2

illustrates the analyze phase with detailed instructions for using Minitab

®

.

The improve and control phases are briey discussed in Section 11.3.

11.1 Define and Measure Phases

Of late, the town has been receiving excessive recyclable trash from its resi-

dents, and hence, the town hall aims to communicate to the residents differ-

ent ways to reuse the recyclables before the residents dispose of them. To this

end, the town hall collects data regarding how much waste of each category

was collected and recycled during the previous year. These data are in the

CHAPTER_11_1.MTW worksheet (the worksheet is available at the publish-

er’s website; the data from the worksheet are also provided in the Appendix).

Figure11.1 is a screenshot of the worksheet.

The town hall rst wishes to identify the categories of waste that contribute

the most to the total waste. A Pareto chart can be used for this purpose, and

Figure11.2 shows how to select a Pareto chart. Doing so will open the dialog

box shown in Figure11.3. Select the “Recycled Trash” column for “Defects

or attribute data in”, and “Number of Tons (in hundreds)” for “Frequencies

in”. Select the option of “Do not combine” so that the categories of waste

are not combined. Clicking on “Options” will open the dialog box shown in

Figure11.4. Enter the X-axis label as “Recycled Trash” and the Y-axis label

as “Number of Tons (in hundreds)”. Also, enter the title of the Pareto chart

as shown. Click on “OK” and it takes you back to the dialog box shown in

Figure11.3. Click on “OK” and the Pareto chart shown in Figure11.5 is the

186 Six Sigma Case Studies with Minitab

®

FIGURE 11.2

Selection of “Pareto Chart”.

FIGURE 11.1

Recycled trash.

187Pareto Chart and Fishbone Diagram to Minimize Recyclable Waste

result. It is clear from the Pareto chart that almost 40% of the recycled waste is

paper. Hence, the town hall decides to focus on minimizing the paper waste.

11.2 Analyze Phase

The employees of the town hall brainstorm to identify the different ways to

minimize the paper waste. They classify paper waste into three types: ofce,

kitchen, and other. The examples of these three types are in the C4, C5, and

C6 columns, respectively, in the CHAPTER_11_2.MTW worksheet (the work-

sheet is available at the publisher’s website; the data from the worksheet are

also provided in the Appendix). Figure11.6 is a screenshot of the worksheet.

Notice that, in addition to the examples in the C4, C5, and C6 columns, a

FIGURE 11.3

Entry of defects and frequencies for Pareto chart.

FIGURE 11.4

Entry of labels for Pareto chart.

188 Six Sigma Case Studies with Minitab

®

separate column is created for each example, where ways to minimize the

waste for that example have been listed. For example, for the “Ofce paper”

example in the C4 column, a separate column (C8) is used to list various

ways (“print on both sides”, “use email instead”, etc.) to minimize waste for

this example.

To facilitate understanding of the above by all the employees, a shbone

diagram can be created. Figure11.7 shows how to select a shbone diagram

(also called a cause-and-effect diagram). Doing so will open the dialog box

shown in Figure11.8. Select the three categories of paper waste for “Causes”

and type in the same names for “Label”, as shown in Figure11.9. Also, com-

plete the “Effect” and “Title” boxes as shown. Moreover, check the box for

“Do not display empty branches”.

Numb

er of Tons (in hundreds)

Percent

Cum %

600

39.5

39.5

260

17.1

56.6

210

13.8

70.4

200

13.2

83.6

200

13.2

96.7

50

3.3

100.0

Recycled Trash

Plastic

Yard Waste

Glass

Iron

Aluminum

Paper

1600

1400

1200

1000

800

600

400

200

0

100

80

60

40

20

0

Number of Tons (in hundreds)

Percent

Pareto Chart for To wn XYZ Project

FIGURE 11.5

Pareto chart.

FIGURE 11.6

Data for paper waste.

189Pareto Chart and Fishbone Diagram to Minimize Recyclable Waste

FIGURE 11.7

Selection of shbone diagram (“Cause-and-Effect”).

FIGURE 11.8

Categories for branches of shbone diagram.