power spectrum estimates for CMB polarization: sampling covariance'
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cosmic microwave background – methods: analytical: – methods: numerical.

Introduction {#sec:intro}
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With the recent results from the Degree Angular Scale Interferometer (DASI; @kovac02 [@leitch04]), the Cosmic Anisotropy Mapper (CAPMAP; @barkats04) and the Cosmic Background Imager (CBI; @readhead04), and the imminent two-year results from the *Wilkinson Microwave Anisotropy Probe* (WMAP; @kogut03), the characterization of the polarization of the cosmic microwave background (CMB) polarization is gathering pace. The ultimate goal of such experiments is to constrain parameters describing the cosmological model and its fluctuations, and hence test models for the generation of these fluctuations, such as inflation. In Gaussian theories, all of the cosmological information encoded in the CMB anisotropies and their polarization is contained in their power spectra. For this reason, estimating CMB power spectra is a useful and efficient form of data compression in analysis pipelines [@bond00]. However, estimating the spectra is not enough: it is also essential to have an accurate covariance matrix, and preferably an accurate model for the shape of the likelihood function (see e.g. @bond00 [@efstathiou04]). Modelling the covariance matrix for a particularly efficient class of polarization power spectra estimators – heuristically-weighted quadratic estimators, or pseudo-$C_l$s 