The Ontario Court of Appeal has a rather prim notice on its website about the authorship of judgments, stating that anything issued 'by the Court' can be assumed to be 'the product of significant contribution by all members of the panel'.

That may well be true in many instances, but an algorithm developed by some wonks in the US could disprove the assertion. 'Algorithmic attribution techniques' have been applied to the language of judgments of the US Supreme Court, identifying with a 'high degree of accuracy' the true authorship of unanimous or disputed opinions, with the potential to reveal the judicial politics behind the scenes.

http://www.ontariocourts.ca/coa/en/about/judgments.htm

http://stlr.stanford.edu/pdf/algorithmicattribution.pdf

http://cognoscenti.wbur.org/2013/07/30/unsigned-per-curiam-opinions-andrew-lo