Attribute Charts – Defects and Rejects Charts
There are four different types of attribute charts. For each type of attribute data, defects and rejects, there is a chart for subgroups of constant size and one for subgroups of varying size.
Remember: Defects Charts count the number of defects within the inspection unit.
Rejects Charts count the number of rejected units in a subgroup.
Defects Charts
The two defects charts are the c chart and the u chart. The c refers to count of defects in a subgroup of constant size. The u is a per unit count within a variable size subgroup.
A mnemonic to help you remember that the c chart represents Defects data is to think back to your school days and the C grade you got in a class when the number of defects or errors within one test exceeded the threshold. Another way to remember which subgroup type goes with which chart is that c is for “constant” and u is for “un-constant”.
