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Minimum sample size question

cal_lim

I’m using JMP Pro 12.1 and have questions that I hope you could help on using JMP to answer them.

Product runs are generating defects.

Mean defect rate = 0.002 (average 1 defect every 500pcs)

Std Dev = 0.01

1. What is the probability of finding at least 1 defect when I random sample 500pcs?

2. What is the minimum sample size I need to sample in order to get at least 1 defect at Alpha = 0.05

3. Is Alpha = 0.05 equivalent to 95% Confidence Interval?

Accepted answers

ron_horne

try this:

Counts per Unit

to get to the platform from the main menu: DOE >> Sample size and power >> Counts per unit.

All comments

ron_horne

try this:

Counts per Unit

to get to the platform from the main menu: DOE >> Sample size and power >> Counts per unit.

cal_lim

Thanks Ron!

From the calculations, I would need 7885 samples to get at least 1 defects at a 95% C.I.

11788_Screen Shot 2016-06-09 at 15.29.28.png

ron_horne

you are welcome @cal_Iim

if this an academic exercise than alpha of 0.05 and power of 0.95 are in place. if on the other hand you need to actually do this to save money in a production scenario i would choose these values based on cost/ benefit. for that you need to know how much does each fault cost to the firm.

in most production cases i came across, 0.05 was very far from optimal (too high or too low).

best,

ron

cal_lim

Cool! Can you give scenarios whereby the alpha of 0.05 was too high or low?

Thanks.