P-chart
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In industrial statistics, the p-chart is a type of control chart that monitors the proportion of nonconforming units in a sample. The appropriate data for p-charts are attribute data (conform or non-conform, yes or no, etc.). The subgroup size should ideally be equal, although unequal sample sizes can be accommodated.
p-chart
- The "p" comes from use of the proportion of nonconforming items
- Need a good definition of nonconforming items – usually a categorical definition
- Can be of equal or unequal subgroups
- Normally need large subgroups – can even be up to total for the period
Control limits for the p-chart are calculated on the basis of the binomial distribution and an approximation based on the central limit theorem.
The control limits for this chart type can be determined by the formula: 
