Quality Magazine

BRAIN TEASER OF THE MONTH

March 1, 2005
enews

c) is the correct response.

Like p-charts, u-charts record attributes data. But the distinction lies in the difference between go/no go situations, where a product either has a defect or it does not, and nonconforming products, which may have several defects in a single product. P-charts collect data relating to the proportion of rejected containers, while u-charts give information about how many individual defects are recorded in samples.

For example, manufactured parts that are the wrong dimension and tested with a go/no-go approach should be charted on a p-chart. Ice cream, on the other hand, might have too many chocolate chips, a sloppy label, and insufficient fill-all in the same container. Instead of recording the ice cream container as good or bad, more useful information would be gathered by identifying the kinds of defects in each container. This could be charted with a u-chart, and future analysis by means of Pareto charts.