#### Title

Attribute Charts for Monitoring a Dependent Process

#### Document Type

Article

#### Publication Date

4-2007

#### Publication Title

Quality and Reliability Engineering International

#### DOI

10.1002/qre.793

#### ISSN

1099-1638

#### Abstract

For some repetitive production processes, the quality measure taken on the output is an attribute variable. An attribute variable classifies each output item into one of a countable set of categories. One of the simplest and most commonly used attribute variables is the one which classifies an item as either ‘conforming’ or ‘non-conforming’. A tool used with a considerable amount of success in industry for monitoring the quality of a production process is the quality control chart. Generally a control charting procedure uses a sequence, of the quality measures to make a decision about the quality of the process. How this sequence is used to make a decision defines the control chart. In order to design a control chart one must consider how the underlying sequence, is modeled. The sequence is often modeled as a sequence of independent and identically distributed random variables. For many industrial processes, this model is appropriate, but in others it may not be. In this paper, a sequence of random variables, is used to classify an item as conforming or non-conforming under a stationary Markov chain model and under 100% sequential sampling. Two different control charting schemes are investigated. Both schemes plot a sequence of measures on the control chart, that count the number of conforming items before a non-conforming item. The first scheme signals as out-of-control if a value of falls below a certain lower limit. The second scheme signals as out-of-control if two out of two values of fall below a certain lower limit. The efficiency of both of the control charts is evaluated by the average run length (ARL) of the chart and the power of the chart to detect a shift in the process. The two out of two scheme is shown to have high power and a large ARL given certain parameter values of the process. An example of the two out of two scheme is provided for the interested reader.

#### Recommended Citation

Shepherd, Deborah K., Charles W. Champ, Steven E. Rigdon.
2007.
"Attribute Charts for Monitoring a Dependent Process."
*Quality and Reliability Engineering International*, 23 (3): 341-365.
doi: 10.1002/qre.793 source: https://onlinelibrary.wiley.com/doi/abs/10.1002/qre.793

https://digitalcommons.georgiasouthern.edu/math-sci-facpubs/493