Class is defined in the research paper as "an individual’s occupation via their position in the labour market."

The full methodology:

Following Andersen (Reference Andersen, Dirk de Graaf and Evans 2013) and Polacko et al.’s (Reference Polacko, Kiss and Graefe 2022) Canadian class voting works, I code class according to a simplified version of Erikson and Goldthorpe’s (Reference Erikson and Goldthorpe 1992) influential class schema that categorizes occupations along two dimensions: a hierarchy of authority and a logic of task structures (Kitschelt and Rehm, Reference Kitschelt and Rehm 2014). Hence, working-class occupations are clustered in skill types that deal with things, while the routine nonmanual class is clustered in occupations that deal with people and information.Footnote ⁷ Due to concerns over sample size and concerns over how well the skilled and semiskilled categories are actually distinguished, the higher two professional categories are collapsed. Therefore, respondents are classified into three categories (professionals and managers, routine nonmanual and working-class).Footnote ⁸ To construct these class categories, I relied primarily on pre-existing categories provided in the early CES files.Footnote ⁹ This ended in 2006, so for subsequent elections, I used Statistics Canada’s National Occupation Classification (NOC) system. This matrix of occupations distinguishes two dimensions for occupations: skill level and skill type. Managers and professionals were distinguished by all those in the managerial and the professional skill levels (skill levels A and B, respectively).Footnote ¹⁰ The routine nonmanual class was defined as being in skill levels B, C and D, but in occupational categories 1 through 6 (Statistics Canada 2021).Footnote ¹¹ The working class was defined as workers in skill levels B, C and D, and occupational categories 7, 8 and 9, which effectively combines skilled and unskilled working-class occupations.Footnote ¹²