What is the test for identifying a "personal characteristic" giving rise to discrimination in an equality claim?

In R v. Swain, 1991 CanLII 104 (SCC), [1991] 1 S.C.R. 933 at p. 992, 3 C.R.R. (2d) 1 at p. 38, Lamer C.J.C. focused on the need to identify a “personal characteristic” giving rise to discrimination in the analysis of an equality claim: …in determining whether the claimant’s s. 15(1) rights have been infringed, the court must consider whether the personal characteristic in question falls within the grounds enumerated in the section or within an analogous ground, so as to ensure that the claim fits within the overall purpose of s. 15: namely, to remedy or prevent discrimination against groups subject to stereotyping, historical disadvantage and political and social prejudice in Canadian society.

In Egan v. Canada, supra, while the court was divided in the result and with respect to certain basic issues of analysis of equality rights, sexual orientation was accepted by all members of the court as an analogous ground of discrimination. La Forest J. found that sexual orientation (at p. 528 S.C.R., p. 90 C.R.R.) “is a deeply personal characteristic that is either unchangeable or changeable only at unacceptable personal costs, and so falls within the ambit of s. 15 protection as being analogous to the enumerated grounds.” Cory J., writing for himself and Iacobucci J. on the point, stated (at p. 599 S.C.R., p. 143 C.R.R.): “The fundamental consideration underlying the analogous grounds analysis is whether the basis of distinction may serve to deny the essential human dignity of the Charter claimant.” Cory J. distanced himself from the “discrete and insular minority” analysis, observing that while this could serve as a useful analytic tool, it was not a prerequisite for finding that the challenged category-did constitute an analogous ground. Adding that (at p. 600 S.C.R., p. 143 C.R.R.) “it may be helpful to see if there is any indication that the group in question has suffered discrimination arising from stereotyping, historical disadvantage or vulnerability to political and social prejudice”, Cory J. found that sexual orientation did constitute an analogous ground.