September 19, 201114 yr Dear All, Please see below a query posted by a past participant. Please feel free to respond to this query. Regards, shantanu kumar --------------x--------------------------x-----------------------x--------------------------x--------------------------x---- Hi Shantanu, Hope you are doing well. I was trying to understand p-charts. Consider a case where in the output is varying and defectives are identified. Data for the same is as follows. When I tried to plot a p-chart for the same in Minitab, the UCL line varies as shown because of varying output, but a value of UCL (0.05439) is highlighted; Similarly for LCL (0.00675). How is this figure arrived at? Defective Volume15 50020 52813 46512 470 Warm Regards,Krishnan S
September 19, 201114 yr The UCL and the LCL shown are for the last data point (i,e, Defective = 12 and Volume = 470). How do we arrive at these figures is as follows 1. First calculate pbar => find out individual proportions and then take the average of the same. 2. Control limits = pbar +- 3 times (square root(pbar(1-pbar)/N), N = sample size for the last sample (if you change the last data point, you UCL and LCL would change).
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