Control charts fall into two categories: Variable and Attribute Control Charts.
- Variable data are data that can be measured on a continuous scale such as a thermometer, a weighing scale, or a tape rule.
- Attribute data are data that are counted, for example, as good or defective, as possessing or not possessing a particular characteristic.
The type of control chart you use will depend on the type of data you are working with.
- It is always preferable to use variable data.
- Variable data will provide better information about the process than attribute data.
- Additionally, variable data require fewer samples to draw meaningful conclusions.