Can you use Avg & Std Dev with Non-Normal Data?

ThaRide · 11-06-2009, 08:13 AM

I know this may be a simple question, but I am reviewing a report where an engineer measured the force of 30 samples and said the Average - 3 Standard Deviations is above teh minimum specifcation (whether thats the best method or not is not the issue, thats another story) but can he even make that statement if the data is not normal. My assumption has always been that if the data is not normal, it must be transformed first, then those calculations can be used

I just determined teh data is not normal and has a Box Cox lambda of -5. How can I now state how good (capable) teh data is?

11-06-2009, 08:13 AM	#1
ThaRide Junior Member Join Date: Jun 2009 Posts: 6 Thanks: 0 Thanked 0 Times in 0 Posts	Can you use Avg & Std Dev with Non-Normal Data? I know this may be a simple question, but I am reviewing a report where an engineer measured the force of 30 samples and said the Average - 3 Standard Deviations is above teh minimum specifcation (whether thats the best method or not is not the issue, thats another story) but can he even make that statement if the data is not normal. My assumption has always been that if the data is not normal, it must be transformed first, then those calculations can be used I just determined teh data is not normal and has a Box Cox lambda of -5. How can I now state how good (capable) teh data is? Last edited by ThaRide; 11-06-2009 at 08:38 AM.

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