Harman Patil (Editor)

Fisher's z distribution

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Fisher's z-distribution

Parameters
  
d 1 > 0 ,   d 2 > 0 {displaystyle d_{1}>0, d_{2}>0} deg. of freedom

Support
  
x ∈ ( − ∞ ; + ∞ ) {displaystyle xin (-infty ;+infty )!}

PDF
  
2 d 1 d 1 / 2 d 2 d 2 / 2 B ( d 1 / 2 , d 2 / 2 ) e d 1 z ( d 1 e 2 z + d 2 ) ( d 1 + d 2 ) / 2 {displaystyle { rac {2d_{1}^{d_{1}/2}d_{2}^{d_{2}/2}}{B(d_{1}/2,d_{2}/2)}}{ rac {e^{d_{1}z}}{left(d_{1}e^{2z}+d_{2} ight)^{left(d_{1}+d_{2} ight)/2}}}!}

Mode
  
0 {displaystyle 0}

Fisher's z-distribution is the statistical distribution of half the logarithm of an F-distribution variate:

z = 1 2 log F

It was first described by Ronald Fisher in a paper delivered at the International Mathematical Congress of 1924 in Toronto. Nowadays one usually uses the F-distribution instead.

The probability density function and cumulative distribution function can be found by using the F-distribution at the value of x = e 2 x . However, the mean and variance do not follow the same transformation.

The probability density function is

f ( x ; d 1 , d 2 ) = 2 d 1 d 1 / 2 d 2 d 2 / 2 B ( d 1 / 2 , d 2 / 2 ) e d 1 x ( d 1 e 2 x + d 2 ) ( d 1 + d 2 ) / 2 ,

where B is the beta function.

When the degrees of freedom becomes large ( d 1 , d 2 ) the distribution approach normality with mean

x ¯ = 1 2 ( 1 d 2 1 d 1 )

and variance

σ x 2 = 1 2 ( 1 d 1 + 1 d 2 ) .
  • If X FisherZ ( n , m ) then e 2 X F ( n , m ) (F-distribution)
  • If X F ( n , m ) then log X 2 FisherZ ( n , m )
  • References

    Fisher's z-distribution Wikipedia