Scale and shape parameters of Gamma mixture distributions

Hello,


I used the function "mix" (package "mixdist'') to fit Gamma mixture distributions. The function gives mu and sigma parameters (output below). How can I find the scale and shape parameters of the Gamma distributions ?


Parameters:
      pi    mu sigma
1 0.2089 185.7 285.4
2 0.7911 530.1 423.5

I have no familiarity with the "mixdist" package, but I find it very 
surprising that mix() would return a fit of a Gamma mixture parametrised 
in terms of mu and sigma.  I suspect that you are doing something wrong.

If it really *does* give you such a parametrisation, you can recover the 
shape (alpha) and scale (beta) parameters by solving

    mu = alpha*beta
    sigma^2 = alpha*beta^2

for alpha and beta.

cheers,

Rolf Turner

Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276