Hi,
I am sorry if my question does not make sense.
The WMAP3 paper, Spergel et al. astroph/0603449 page 7, says: "that the reduced \chi_{\rm eff}^2 is 1.041 for the combined TT and TE data (1410 D.O.F., including TE l=24450), quarter of the detected EE signal." So I would expect that the \chi^2 is 1.041*1410=1467.81. But I usually get the \chi^2=11266. I think I misunderstand something. What is wrong here?
I set the num_cls=3 as default. So cosmomc should include TT, TE, and EE. Is it the reason why I got a large number of \chi^2? However, I also set num_cls=3 in July 2005 version of cosmomc and WMAP1 data; in that case, I got best fit values and \chi^2 very close to those given by WMAP1 paper.
I use the \Lambda CDM model; most parameters and options are default. I am using April 2006 version.
Thanks!
Loison Hoi
21 Apr 2006
Cosmomc: the reduced \chi^2

 Posts: 23
 Joined: February 21 2006
 Affiliation: McGill University

 Posts: 1543
 Joined: September 23 2004
 Affiliation: University of Sussex
 Contact:
Re: Cosmomc: the reduced \\\\chi^2
It depends on what you mean by the chisquared. The chisquared over pixels is different from the chisquared over C_l. Since the WMAP3 likelihood code mixes pixelspace and C_l likelihood approximations, the absolute value of 2log(Liklihood) doesn't have a very obvious interpretation. See the readme.txt supplied with the WMAP likelihood code for the breakdown.
I guess the quoted chisquareds are using some C_l likelihood approximation for all l?
I guess the quoted chisquareds are using some C_l likelihood approximation for all l?

 Posts: 23
 Joined: February 21 2006
 Affiliation: McGill University
Cosmomc: the reduced \\chi^2
Hi Antony,
Thanks for your clarification!
Loison Hoi
22 Apr 2006
Thanks for your clarification!
Loison Hoi
22 Apr 2006