HuskerP7M8
posted this
25 January 2017
Hi Joe,
After I read your post and looked at the group ES (Extreme Spread) for the 25 groups you shot, it didn't appear to me that the variation in ES was abnormal. Since I was curious, I decided to conduct a very simple check to possibly verify if your group sizes and group size averages varied more than we would expect to see.
Are you familiar with the term COV (Coefficient Of Variation)?
Again, to keep this very simple, for those who aren't statistical nerds like me, the COV varies based on the number of shots used to form each group.
It's an easy calculation that's nothing more than the Standard Deviation divided by the Average, and if you use Excel, format the cell which contains the formula as a percentage. The end result is a percentage that tells you how much variation, on average, you can expect to see when shooting a string of groups.
In your case, using 5-shot groups, the COV should be approximately 25%.
If you had used 2-shot groups in your testing, the COV would be expected to be approximately 50%. And, the COV will be different for 3-shot groups, 10-shot, 25-shot, 50-shot, etc.
Take a look at the Excel chart below using your data and notice that the COV, on average, is 28.7%. That's very close to the expected COV using 5-shot groups and will converge closer to the 25% value as the size of the sample increases.
There are many other better statistical tools available to determine if your variation is excessive, but COV is the simplest to understand and easiest to use.
Landy
“In God we trust; all others must bring data.” “Without data, you're just another person with an opinion.” “If you can't describe what you are doing as a process, you don't know what you're doing.” “It is not enough to do your best, you must know what to do, and then do your best.” W. Edwards Deming (October 14, 1900 - December 20, 1993)