Quality Quiz:

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Note: Last month’s Quality Quiz (using nominal variables in multiple regression) prompted a number of e-mails about the use of this technique, as well as questions from a customer who happens to be Black Belt certified. His question prompted this month’s quiz topic, which defines types of data.

Raney Daye is head of the quality assurance team for Never a Dry Moment, Inc., a manufacturer of components for windshield-wiper units produced for the Big Three auto companies. His team has been collecting data related to the proper dimension of the cavity of a windshield wiper button.

Every hour, 100 buttons are selected as samples, and with a go/no go gage, they are checked by a member of the quality team. After three days, the data is brought to Raney for analysis. It consists of 24 percentages of good parts (e.g., .01, .025, .011…), on the basis of which Raney decides that he will do an individuals moving range chart to determine whether the process is in control.

One of the team members, Carla Fornia, who believes herself to be a greater authority on chart types than Raney Daye could ever be, challenges this decision. “This is not the right chart to use for this kind of data,” she declares loudly. Raney wants to assert his authority, and responds that because this is clearly interval data, an individuals moving range chart is obviously the right choice. “Anyone knows that,” he adds. Carla goes back to work, seething at the insult.

To know who’s right, we must determine the kind of data that these samples reflect.

Which of the following is correct?

a) Interval (variable) data

b) Ratio (attribute) data

c) Nominal data

d) Ordinal data

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