# Reply To: What is standard deviation?

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“oldspook”Some folks would say that only a 100% probability of a hit is acceptable and so we should consider the ES to be the determining factor. The ES is a property of the string it represents and is statistically less significant than the SD because it is composed of only 2 samples in the sample set. If you use the ES of one string, the next string you shoot will almost certainly have a different ES, it might be larger or smaller but because it is only 2 samples from the sample set it will vary more widely than the Standard Deviation from set to set. So you would probably need to shoot a large number of strings to find out what your true maximum ES was… and then you would be into doing the Standard Deviation of your Extreme Spread… probably more pain than gain at that point.

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All good info.

100% probability of a hit?

*“Some folks would say that only a 100% probability of a hit is acceptable and so we should consider the ES to be the determining factor.”*

They are dreaming.

ES tells you what you just did. SD tells you the probability of the next shot (predictive).

That shot string #2 was contrived but you would not know that without the SD. I could contrive a realistic target where shots string #1 gets an 80% hit rate. And shot string #2 misses every time. The ES does not tell you that, but the SD does.

Is an MOA rifle one that hits 100% of shots inside of an inch circle? 100% of your last shot group might be inside of a 1 inch circle. That tells you what you just did (like ES). I consider an MOA gun to be one where the dispersion SD is 1/2moa. That tells me that 68% of the shots will be inside of an inch circle.

I prefer to see both ES and SD. But, if given SD of the last string, I really don’t need the ES.

"oldspook"Some folks would say that only a 100% probability of a hit is acceptable and so we should consider the ES to be the determining factor. The ES is a property of the string it represents and is statistically less significant than the SD because it is composed of only 2 samples in the sample set. If you use the ES of one string, the next string you shoot will almost certainly have a different ES, it might be larger or smaller but because it is only 2 samples from the sample set it will vary more widely than the Standard Deviation from set to set. So you would probably need to shoot a large number of strings to find out what your true maximum ES was... and then you would be into doing the Standard Deviation of your Extreme Spread... probably more pain than gain at that point. ...All good info. 100% probability of a hit?

*"Some folks would say that only a 100% probability of a hit is acceptable and so we should consider the ES to be the determining factor."*They are dreaming. ES tells you what you just did. SD tells you the probability of the next shot (predictive). That shot string #2 was contrived but you would not know that without the SD. I could contrive a realistic target where shots string #1 gets an 80% hit rate. And shot string #2 misses every time. The ES does not tell you that, but the SD does. Is an MOA rifle one that hits 100% of shots inside of an inch circle? 100% of your last shot group might be inside of a 1 inch circle. That tells you what you just did (like ES). I consider an MOA gun to be one where the dispersion SD is 1/2moa. That tells me that 68% of the shots will be inside of an inch circle. I prefer to see both ES and SD. But, if given SD of the last string, I really don't need the ES.