### [astro-ph/0605004] Model selection forecasts for the spectra

Posted:

**May 02 2006**This paper looks at how well Planck can do at distinguishing n_s \ne 1 models from n_s=1.

Why are the authors using the Gaussian likelihood in Eq. 1 rather than the true likelihood function? It is well known that the Gaussian approximation is not very good, and the true function is just as easy to compute with an effective full sky. (it's given explicitly in e.g. Eq 5 of astro-ph/0502469, though I certainly wasn't the first to write it down). Do you get out the correct posterior constraints using this function?

Why are the authors using the Gaussian likelihood in Eq. 1 rather than the true likelihood function? It is well known that the Gaussian approximation is not very good, and the true function is just as easy to compute with an effective full sky. (it's given explicitly in e.g. Eq 5 of astro-ph/0502469, though I certainly wasn't the first to write it down). Do you get out the correct posterior constraints using this function?