Interpretation & Calculations
What is attribute data? Attribute data is also known as "count" data. Typically, we will count the number of times we observe some condition (usually something we do not like, such as an error) in a given sample from the process. This attribute data definition is different from measurement data in its resolution. Attribute data has less resolution, since we only count if something occurs, rather than taking a measurement to see how close we are to the condition. For example, Attributes data for a health care process might include the number of patients with a fever, whereas Variables data for the same process might be the measurement of the patient temperature.
Thus, Attributes data generally provides us with less information than measurement (variables) data would for the same process. Thus, for attributes data, we will generally not be able to predict if the process is trending towards an undesirable state, since it is already in this condition.
Learn more about the SPC principles and tools for process improvement in Statistical Process Control Demystified (2011, McGraw-Hill) by Paul Keller, in his online SPC Concepts short course (only $39), or his online SPC certification course ($350) or online Green Belt certification course ($499).