Charts For Attributes Such As (P,c Charts)

Introduction:

Control charts may be used partly to control variation and partly in the identification and control of the causes which give rise to these variations.

ATTRIBUTE CONTROL CHARTS:

There are four types of attribute control chart:

• The attribute control charts are classified into the four groups depending on what kind of measurements is being used. The simplest control charts to use are the np chart and the c chart because the number of non-conforming units or non-conformities is charted.
• It is a drawback, however, that the sample size must be constant for these simple charts. The charts to measure and analyze proportions are a little bit more difficult to use but both can adjust for varying sample sizes. Some further explanations will be given below.

P-Chart:

•  The p chart is a control chart to analyze and control the proportion of failures or defects in subgroups or samples of size n. This control chart, as well as the np chart, is based on assumptions such as the binomial distribution.

Np Chart:

• The np chart is a control chart to analyze and control the number of failures or defects in subgroups or samples of size n.

C-Chart:

• The c chart is a control chart to analyze and control the number of non-conformities (defects, failures) with a constant sample size. The difference from the np chart is that for each unit inspected there are more than two mutually exclusive outcomes.