Process Control with Attribute Measurement:

Measurement through attributes implies that samples are taken on the basis of single decision that means item is either good or bad. As, the answer would be yes or no, we may use simple statistics to make p chart with an upper control limit (UCL) or lower control limit (LCL). We can draw these control limits on a graph and then plot the fraction defective of each individual sample tested. Although, following mathematical equations may be utilized to determine the UCL or LCL.

p¯ = Total number of defects from all samples / (Number of samples × Sample size)

 UCL = p¯ + z s _p         

LCL = p¯ - z s _p

where,  p¯ is the fraction defective, s_p is the standard deviation, n is the sample size and z is the number of standard deviations for specific confidence.