Attribute Charts

There are four main types of attribute chart which differ in the type of data which they are used to record. Before listing the charts it will be useful to provide a couple of definitions:

Defects are errors in the output of a process, for example:

Defectives are items which, because of the presence of one or more defects are considered faulty and unfit for use. Examples include:

For a given sample, the number of defective items cannot be larger than the sample size. However, the number of defects found within the sample is potentially infinite.

The four main attribute charts are:

In addition the XmR chart can be used as a generic 'catch-all' chart for any attribute data. It is not as sensitive as the more specific charts, but means you don't have to try and decide which is the appropriate chart for a given situation. If in doubt, the XmR chart will give more reliable results than the wrong type of attribute chart.

In this course we will only be looking in detail at the u-Chart.