Degree of polarization across Si ii λ6355 as a function of light curve decline rate. Our measurements of SN 2005hk are shown in red, with the value of Δ P(Si ii) indicated by the point with the heavy outline, data in black are taken from Wang et al. (2007), the measurement for SN 2006X (▵) is from Patat et al. (2009), the measurement for the luminous event SN 2009dc ( ) is taken from Tanaka et al. (2010), and the measurement for SN 2005ke (×) is taken from F. Patat et al. (2010, in preparation).