Methods and formulas for P Chart

Select the method or formula of your choice.

Plotted points

Each plotted point represents the proportion of defectives for one subgroup, p_i:

Data points on a P chart follow the binomial distribution.

Term	Description
x_i	number of defectives for subgroup i
n_i	size of subgroup i

The center line represents the proportion of defectives for your process,

. If you do not specify a historical value, then Minitab uses the average proportion of defectives from your data,

, to estimate

Term	Description
	number of defectives in subgroup
	size of subgroup

The LCL for each subgroup is equal to the greater of the following:

The UCL for each subgroup is equal to the lesser of the following:

Term	Description
	process proportion
	parameter for Test 1. The default is 3.
	size of subgroup