ABSTRACT
Chapter 8 introduces the underlying concepts behind using attribute data, distinguishes between the various types of attribute data and describes in detail the use of control charts for attributes: np-, p-, c- and u-charts.
Attributes, things that are counted and are generally more quickly assessed than variables, are often used to determine quality. These require different control methods to those used for variables. Attributes may appear as numbers of non-conforming or defective units, or as numbers of non-conformities or defects.
It is vital, as always, to define attribute specifications. The process capabilities may then be determined from the average level of defectives or defects measured. Improvements in the latter require investigation of the whole process system. Never-ending improvement applies equally well to attributes, and variables should be introduced where possible to assist this.
Attribute data is frequently found in non-manufacturing; for example, activity sampling is a technique based on similar theory and is used to obtain a realistic picture of time spent on particular activities. Attribute control charts may be useful in the analysis of absenteeism, invoice errors, etc.
