2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/13150We discuss the problem of constraining cosmological parameters with cosmic microwave background band--power estimates. Because these latter are variances, they do not have gaussian distribution functions and, hence, the standard $χ^2$--approach is not strictly applicable. A general purpose approximation to experimental band--power likelihood functions is proposed, which requires only limited experimental details. Comparison with the full likelihood function calculated for several experiments shows that the approximation works well.To be published in ``The CMB and the Planck Mission'', proceedings of a workshop held in Santander, Spain, June 1998Astrophysicstext