Variable and attribute data

measured values versus counts

Variable data are measured on a continuous scale, such as length, torque or temperature. Attribute data are counted or classified, such as good or bad, or the number of defects.

Variable data carry more information, so they need fewer samples and allow Cpk and X-bar charts. Attribute data need p, np, c or u charts and larger samples.

Calculate it

Attribute Control Charts: p, np, c and u charts for defectives and defects, including variable sample sizes.

Related terms

• p chart: control chart for the proportion defective
• I-MR chart: individuals and moving range chart
• Defect and defective: a flaw versus an unusable unit