How many units to sample test? Temperature Testing

[JamieMcIlroy]

I have built 250 units and temperature tested a sample of 20 – unfortunately giving me 3 failures at elevated temperature.
How many units should I sample out of the 250 to be 95% confident that the failure rate is no worse than 15%?

 

[Marc]

Can anyone help with this? My Thanks! in advance!

 

[Tim Folkerts]

There is a discussion of the topic in this thread. I also posted a spreadsheet there that will do such calculations

The short answer is that if you test 19 units and find no defects, then you can be 95% confident that 85% of the units are good.


Tim F

 

[JamieMcIlroy]

Spot on.. thanks very much Tim