Difference between revisions of "Closed Form Precision"

From ShotStat
Jump to: navigation, search
Line 1: Line 1:
 
[[Measuring Precision]] showed how a single parameter ''σ'' characterizes the precision of a shooting system.
 
[[Measuring Precision]] showed how a single parameter ''σ'' characterizes the precision of a shooting system.
  
This ''σ'' is the parameter for the Rayleigh distribution with probability density function <math>\frac{x}{\sigma^2}e^{-x^2/2\sigma^2}</math>.
+
This ''σ'' is the parameter for the Rayleigh distribution with probability density function <math>\frac{x}{\sigma^2}e^{-x^2/2\sigma^2}</math>.  The associated Cumulative Distribution Function gives us the probability that a shot falls within a given radius of the center:
 +
:<math>Pr(r \leq \alpha) = 1 - e^{-\alpha^2 / 2 \sigma}</math>
 +
Therefore, we expect 39% of shots to fall within a circle of radius ''σ'', 86% within ''2σ'', and 99% within ''3σ''.
  
 
Using the characteristics of the Rayleigh distribution we can immediately compute the three most useful [[Describing_Precision#Measures|precision measures]]:
 
Using the characteristics of the Rayleigh distribution we can immediately compute the three most useful [[Describing_Precision#Measures|precision measures]]:
Line 11: Line 13:
 
:<math>MR_n = \sigma \sqrt{\frac{\pi}{2 c_{B}(n)}}\ = \sigma \sqrt{\frac{\pi (n - 1)}{2 n}}</math>
 
:<math>MR_n = \sigma \sqrt{\frac{\pi}{2 c_{B}(n)}}\ = \sigma \sqrt{\frac{\pi (n - 1)}{2 n}}</math>
  
Circular Error Probable <math>CEP = \sigma \sqrt{\ln(4)}</math>
+
Circular Error Probable <math>CEP = \sigma \sqrt{\ln(4)}</math>.

Revision as of 14:35, 19 November 2013

Measuring Precision showed how a single parameter σ characterizes the precision of a shooting system.

This σ is the parameter for the Rayleigh distribution with probability density function \(\frac{x}{\sigma^2}e^{-x^2/2\sigma^2}\). The associated Cumulative Distribution Function gives us the probability that a shot falls within a given radius of the center: \[Pr(r \leq \alpha) = 1 - e^{-\alpha^2 / 2 \sigma}\] Therefore, we expect 39% of shots to fall within a circle of radius σ, 86% within , and 99% within .

Using the characteristics of the Rayleigh distribution we can immediately compute the three most useful precision measures:

Radial Standard Deviation \(RSD = \sigma \sqrt{2}\). The expected sample RSD of a group of size n is \[RSD_n = \sigma \sqrt{\frac{2}{c_{G}(n)}} \approx \sigma \sqrt{2 - \frac{1}{2n} - \frac{7}{16n^2} - \frac{19}{64n^3}}\]

Mean Radius \(MR = \sigma \sqrt{\frac{\pi}{2}}\). The expected sample MR of a group of size n is \[MR_n = \sigma \sqrt{\frac{\pi}{2 c_{B}(n)}}\ = \sigma \sqrt{\frac{\pi (n - 1)}{2 n}}\]

Circular Error Probable \(CEP = \sigma \sqrt{\ln(4)}\).