CosmoCoffee

Posted: **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_&#123;\rm lensing&#125;
     0.7639290E+03     \chi^2_&#123;\rm plik&#125;
     0.1049659E+05     \chi^2_&#123;\rm lowTEB&#125;
     0.2068837E+01     \chi^2_&#123;\rm prior&#125;
     0.1128631E+05    \chi^2_&#123;\rm CMB&#125;

While comparing two models which one should I use?

Any insight will be very helpful.

Thanks,
Brajesh

Posted: **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

CosmoCoffee

Meaning of different chi-squares in COSMOMC

Meaning of different chi-squares in COSMOMC

Meaning of different chi-squares in COSMOMC