Consequently, the Court characterizes equality as a dynamic concept whereby the "accommodation of differences...is the essence of true equality."⁴⁷ The purpose of s. 15 is therefore twofold; to prevent discrimination, and to ameliorate disadvantages experienced by groups and individuals who have historically been excluded from mainstream society, as has been the case for persons with mental disabilities.

In assessing an equality claim under s. 15 of the Charter the Court looks beyond the actual law being challenged, and considers the social, political and legal position of the claimant in society.⁴⁸ Clearly, legislatures must have the authority to draw distinctions among people. However, according to the Court's interpretation of the equality guarantee in the Charter, such distinctions must not exacerbate or re-enforce the disadvantage of certain groups and individuals in society.⁴⁹ To be more specific, the Court has stated that the overall purpose of s. 15 is to "...remedy or prevent discrimination against groups subject to stereotyping, historical disadvantage and political and social prejudice in Canadian society."⁵⁰ Consequently, social context is the key to any equality rights analysis.

In a 1999 ruling, the SCC confirmed the need for a purposive and contextual approach to s. 15 claims.⁵¹ The Court stated that the following three inquiries should be made when evaluating the merits of a claim of discrimination under the Charter:

1. Does the impugned law impose differential treatment, in purpose or effect, on the claimant compared to others?

2. Is the claimant subject to differential treatment based on one or more of the enumerated and analogous grounds?

3. Does the law in question have a purpose or effect that is discriminatory in the sense that it denies human dignity or treats people as less worthy on one of the enumerated or analogous grounds?⁵²

In the Swain case, the SCC recognized persons with mental disabilities as a group in our society which has been negatively stereotyped and historically disadvantaged.⁵³ Practices within the prison system that exacerbate or do not take into account the already disadvantaged position of persons with mental disabilities could be construed as fulfilling the first inquiry of the s. 15 test for discrimination. To answer the second inquiry of the s. 15 test, the claimant must show that a distinction is being drawn between her and others. Typically, this involves comparing the claimant's experiences with that of others.

Determining the appropriate comparator group for FSW with mental disabilities is complex and difficult. There are a number of groups that could be identified as the appropriate comparator group including non-disabled women in the general population, women with mental disabilities in the general population, non-disabled incarcerated FSW, and incarcerated federally sentenced men with mental disabilities. Each group raises its own set of problems which, in the end, results in an artificial and unproductive analysis.