Meaning of different chi-squares in COSMOMC
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Brajesh Gupt
- Posts: 6
- Joined: January 04 2015
- Affiliation: Pennsylvania State University
Post
by Brajesh Gupt » September 02 2016
Hi,
After running getdist, one usually gets the several different types of chi-square values. What do they mean? For example, I get (I show only the best fit values) following 5 types:
Code: Select all
0.2579038E+02 \chi^2_{\rm lensing}
0.7639290E+03 \chi^2_{\rm plik}
0.1049659E+05 \chi^2_{\rm lowTEB}
0.2068837E+01 \chi^2_{\rm prior}
0.1128631E+05 \chi^2_{\rm CMB}
While comparing two models which one should I use?
Any insight will be very helpful.
Thanks,
Brajesh
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Stéphane Ilic
- Posts: 17
- Joined: February 11 2014
- Affiliation: IRAP Toulouse
Post
by Stéphane Ilic » September 30 2016
Hello Brajesh,
Those are the different contributions to the total likelihood/chi2.
From what you copy-pasted, I guess that you ran a MCMC chain with the Planck low-ell ("lowTEB"), high-ell ("plik"), and lensing ("lensing"). The "prior" chi2 is, you guessed it, the contribution coming from the priors you have chosen. The "CMB" chi2 is just the sum of all CMB-related chi2, i.e. "lowTEB+plik+lensing".
You should most likely use the total chi2/likelihood when comparing models...
Cheers,
Stephane