Which control chart is based on proportions?

The p-chart is specifically designed to monitor the proportion of defective items in a process. It is categorized under control charts used for attributes data, which means it focuses on qualitative data that can be classified into categories, such as defective or non-defective.

In the context of quality control, the p-chart tracks the fraction of nonconforming units in a sample over time. For instance, in a manufacturing process, you may want to keep an eye on the proportion of products that do not meet the required standards. By plotting these proportions on a p-chart, you can easily identify trends or variations that may indicate a need for corrective action.

This method is particularly beneficial in identifying whether the quality level of a process is stable or if it is undergoing any shifts. It provides insights on how often defect rates may fluctuate, thereby enabling organizations to ensure consistent quality in their products or services.

Other chart types mentioned serve different functions within statistical process control. The x̄ chart tracks the average of a continuous variable, the R-chart monitors the range of variation, and the s-chart focuses on the standard deviation of a process. These charts are used for different data types and quality measures, which is why the p-chart is the relevant choice for tracking proportions specifically.