You want to determine the control lines for a p-chart for quality control purposes.If the total number of defects from all samples is 2,500, the number of samples is 100, and the sample size is 50, which of the following would be the standard deviation used in developing the control lines?
A)0.4900
B)0.2499
C)0.1556
D)0.0707
E)0.02499

Question

Quizplus · Accepted Answer

The standard deviation for a p-chart is calculated using the formula: sqrt[(p(1-p))/n], where p is the proportion of defects (total defects/total observations) and n is the sample size. Here, p = 2500/(100*50) = 0.5, and n = 50. So, the standard deviation is sqrt[(0.5(1-0.5))/50] = 0.0707.

You Want to Determine the Control Lines for a P-Chart