The AstroStat Slog

The Χ² distribution plays an incredibly important role in astronomical data analysis, but it is pretty much a black box to most astronomers. How many people know, for instance, that its form is exactly the same as the γ distribution? A Χ² distribution with ν degrees of freedom is

p(z|ν) = (1/Γ(ν/2)) (1/2)^ν/2 z^ν/2-1 e^-z/2 ≡ γ(z;ν/2,1/2) , where z=Χ².

Continue reading ‘chi-square distribution [Eqn]’ »

Some statistics papers were listed at the top, of which topics would interest some slog subscribers.
Continue reading ‘[ArXiv] 5th week, Jan. 2008’ »

Only three papers this week. There were a few more with chi-square fitting and its error bars but excluded. Continue reading ‘[ArXiv] 4th week, Jan. 2008’ »

From arxiv/math.st:0708.0169v1
Data-Driven Goodness-of-Fit Tests by L. Mikhail

Goodness-of-Fit tests have been essential in astronomy to validate the chosen physical model to observed data whereas the limits of these tests have not been taken into consideration carefully when observed data were put into the model for estimating the model parameters. Therefore, I thought this paper would be helpful to have a thought on the different point of views between the astronomers’ practice of goodness-of-fit tests and the statisticians’ constructing tests. (Warning: the paper is abstract and theoretical.)
Continue reading ‘[ArXiv] Data-Driven Goodness-of-Fit Tests, Aug. 1, 2007’ »