# Difference between revisions of "Talk:Circular Error Probable"

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[[User:Herb|Herb]] ([[User talk:Herb|talk]]) 16:34, 2 June 2015 (EDT) | [[User:Herb|Herb]] ([[User talk:Herb|talk]]) 16:34, 2 June 2015 (EDT) | ||

− | : ''True, we can sample the POI, but there exists a true POI. We can use the true POI in our models | + | : ''True, we can sample the POI, but there exists a true POI. We can use the true POI in our models regardless of whether we can sample or estimate it in practice. That's true of many of the variables and measures discussed throughout the site: There is a true value we may (or may not) be able to estimate, and then there are sample values (which may be used to estimate the true value). [[User:David|David]] ([[User talk:David|talk]]) 16:39, 2 June 2015 (EDT)'' |

## Revision as of 16:42, 2 June 2015

I think the section on "Systematic Accuracy Bias" misses the point.

Consider two experiments.

(1) Sight weapon then Shoot 10 groups

(2) (a)Sight weapon then shoot group (b) do (a) 10 times

Method (1) has accuracy bias but method (2) does not.

Herb (talk) 18:53, 1 June 2015 (EDT)

- Here's my take: "Systematic accuracy bias" on this page means that the true center of the shot distribution is different from the point of aim (POA). The CEP-radius can then be calculated around two possible centers - either a) around the known POA, or b) around the unknown true distribution mean.
- a) takes into account systematic accuracy bias because the further away the true center of the shot distribution is from the POA, the larger the CEP around the POA becomes, holding distribution spread constant. b) does
*not*take into account systematic accuracy bias because CEP does not vary with increasing distance from true group center to POA, holding distribution spread constant. - In a) only distribution spread (or the full covariance matrix) has to be estimated from observed data, in b) the true center also has to be estimated.
- Any help in getting this issue better across is highly appreciated.

RE: **The CEP-radius can then be calculated around two possible centers - either a) around the known POA, or b) around the unknown true distribution mean.** from above.

The wiki in general uses a third point, the \(\overline{POI_{sample}}\), from which the measurements are calculated. It is the only point for which an actual measurement can be obtained from the sample of shots.

All in all semantics, but the wiki ought to be consistent unless there is some reason to deviate. If a deviation is required, then it should be explicitly stated.

Herb (talk) 16:34, 2 June 2015 (EDT)

*True, we can sample the POI, but there exists a true POI. We can use the true POI in our models regardless of whether we can sample or estimate it in practice. That's true of many of the variables and measures discussed throughout the site: There is a true value we may (or may not) be able to estimate, and then there are sample values (which may be used to estimate the true value). David (talk) 16:39, 2 June 2015 (EDT)*