Question

Effective process control distinguishes between attribute and variable data.  

• Describe some attribute data and variable data, as defined by the author, and label which category includes quantitative vs qualitative variation and how this applies to control charts?

Answer 1

Attribute data:

Attribute data includes various attribute and that suppose to tell us whether the system meeting its requirement or specifications or not. Here, we will count and categorize such data in the form of either defects or defectives. For example: we are measuring a system by giving assessment result either pass or fail, here, pass and fail both are attributes and pass means system meeting its requirements and fail means system does not meet its requirements.

Variable Data:

we use variable data where we measure a process by taking some device or inspector, who will finally measure various process parameters. For example: we are measuring water flow rate of a water jet cutting process, knowing such flow rate over the various run times, we can build necessary control chart to evaluate whether that process is in statistical control or not.

Qualitative variation

Quantitative Variation

It is termed as discontinuous variation and here, we will find various distinct categories For example, we can measure system to get discrete data, like a system could be either pass or fail; such data variation can be presented by using Bar Graph.

It is termed as continuous variation and here, we may not get have distinct categories For example, we can show such Quantitative Variation by using either continuous or discrete variation, here, we will build line graph to show such variation. There are several control charts to show Quantitative Variation, we can use continuous chart like X bar R Chart, I-MR chart to show process variation and we can also use P chart, C chart to show variation associated with defectives and defects accordingly. Here, P chart and C chart would include discrete categories using qualitative measure. The variation could be common cause or assignable cause, assignable causes are such causes due to which we will find big variation and process data will not follow control chart conditions.