Talk:Precision Models

Herb 4/19/2015:

1. I'd rename this page "Models for Precision". Done David (talk) 16:37, 22 April 2015 (EDT)
2. "We have four options for measuring and analyzing precision:" Wrong. There are zillions of options. Good point. Corrected David (talk) 16:37, 22 April 2015 (EDT)
3. "General Bivariate Normal" is not "The normal, a.k.a. Gaussian, distribution." Is it a two dimensional distribution which is somewhat analogous to the one dimensional distribution.
   • Symmetrical meaning SD(V) = SD(H) vs Unsymmetrical meaning SD(V) <> SD(H)
   • Correlated meaning ρ <> 0, vs Uncorrelated meaning ρ = 0.

   So there are 4 cases. (Symmetrical Uncorrelated Bivariate Normal is a special case known as Rayleigh Distribution.)

4. "Statistical Analysis of Dispersion #1. The Closed Form Precision model requires that we assume the shot group is, or can be normalized to be, a fairly symmetric bivariate Gaussian process, but allows for the most convenient estimators and analysis. Therefore, whenever σx≈σy we prefer this approach." This is just wrong. "Closed form" means that integrals of the PDF exists so that a CDF can be calculated. The Radial Standard Deviation is a closed form model, Extreme Spread (aka group size) is not.

   I don't understand the complaint. The Closed Form Precision model is closed form. Extreme Spread is treated separately. David (talk) 16:37, 22 April 2015 (EDT)

5. "Statistical Analysis of Dispersion #2. Circular Error Probable disregards any ellipticity in the actual shot process in order to characterize precision using a single parameter." Not really true. Circular Error Probable assumes no ellipticity. If you apply model incorrectly and get burned then that is your problem, not a fault of the model.

   We are describing the distinguishing characteristics of the model, so I don't see the problem here. David (talk) 16:37, 22 April 2015 (EDT)

6. "Statistical Analysis of Dispersion #4. Extreme Spread and the other Range Statistics, which increase with group size n, do not have any useful functional forms." First group size is used incorrectly again here to mean the Number of shots per group. Second there are not any "Closed Forms" for the distributions. So functions must be evaluated via Monte-Carlo sampling rather than integrated. "Functional forms" is an undefined concept.

   Fixed the first problem. Functional forms are the opposite of empirical forms like Monte-Carlo methods. Is there a better way to phrase that? David (talk) 16:37, 22 April 2015 (EDT)

7. Overall I'd remove "Statistical Analysis of Dispersion" and "Tools" section from page if renamed to "Models For precision."
8. If page was renamed to be for models, then I add section for Error Propagation and move that discussion from "What is Precision?" page here.