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 560, the number of samples is 70, and the sample size is 80, which of the following would be the standard deviation used in developing the control lines?
A) 0.9000
B) 0.4556
C) 0.0335
D) 0.0011
E) 0.0112

Question

Quizplus · Accepted Answer

The formula for calculating the standard deviation for a p-chart is sqrt(p*(1-p)/n), where p is the proportion of defects and n is the sample size.

First, we need to calculate the overall proportion of defects:
p = total defects / (total samples * sample size) 
p = 560 / (70 * 80) 
p = 0.1

Then, we can plug in p and n into the formula for standard deviation:
sqrt(0.1 * 0.9 / 80) = 0.0335

Therefore, the standard deviation used in developing the control lines is 0.0335, which is answer choice C.

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