Relative likelihoods of τ from the stand‐alone exact likelihood code and the first‐year analysis. For the 3 year results, all parameters except τ and the scalar normalization, A, were held fixed as described in the text. The solid curves (labeled "WMAP 3 years") show the exact likelihood for the QV and KaQVW combinations for the combined EE and TE data. If the K‐band directions had been used for the dust polarization template (§ 4.3), leading to inferior cleaning, the likelihood curve would peak where the KaQVW does and have the width of the QV curve. The similarity indicates that any foreground contamination is small. The two broadest curves are from Spergel et al. (2003) and show the first‐year likelihood for the WMAP data alone and for WMAP in combination with other data sets. The dotted line is τ likelihood for the first‐year TE data as reported in Kogut et al. (2003). The curve has a mean of ﹩\tau =0.17﹩ and width ﹩\sigma =0.04﹩.