Question

The control chart for a number of defects in a welded joint is

• A. $\bar{X}$–chart
• B. R–chart
• C. c–chart
• D. p–chart

Hint:

Use a c-chart when counting number of defects; use a p-chart when counting fraction defective.

Answer 1

The Correct Option is C

Control charts are selected based on the type of quality data being monitored. When counting the number of defects or flaws appearing in a welded joint, the data belong to the class of count data, where the count may take any non-negative integer value. A c-chart is specifically used for monitoring the number of defects per inspection unit when the inspected area or opportunity is constant. Here, each welded joint represents one constant-size inspection unit, so a c-chart is the correct statistical tool. Other charts such as $\bar{X}$-chart and R-chart measure continuous variables like dimensions, while the p-chart is used for proportions of defective items, not the number of defects.