Approximating the likelihood function of CMB experiments

We discuss the problem of constraining cosmological parameters with cosmic microwave background band-power estimates. Because these latter are varianc es, they do not have gaussian distribution functions and, hence, the standa rd chi(2)-approach is not strictly applicable. A general purpose approximat ion to experimental band-power likelihood functions is proposed, which requ ires only limited experimental details. Comparison with the full likelihood function calculated for several experiments shows that the approximation w orks well.