Thread: P-chart with probability limits. Please help.

1. A process produces rubber belts in lots of size 2500. Inspection records on the last 20 lots reveal
the following data:
Lot number No. of nonconforming belts Lot number No. of nonconforming belts (The spacing is a bit messed up since I copied and pasted)
1 230 11 256
2 235 12 294
3 221 13 285
4 246 14 231
5 230 15 198
6 227 16 216
7 285 17 231
8 211 18 269
9 242 19 221
10 208 20 207
a. Set up a p- chart with 3 sigma limits to control the process. Estimate the process fraction
nonconforming. Is this an appropriate chart for this process? Explain.
b. Set up a p- chart with probability limits (α = 0.004 ) and estimate again the process fraction
nonconforming. Explain the difference between your answers in 1a) and 1b), if any.


OK. I understand part a. But have no clue about part b. Please help. If you can just tell me the methods or formulas that would be great.

Thank you.

A little help would be appreciated. Just on part b.