L. Marvin Overby, Raymond Tatalovich and Donley T. Studlar, "Party and Free Votes in Canada: Abortion in the House of Commons," Party Politics, 4 (July 1998), 381-392.

First Paragraph:
In recent decades, the traditional scholarly consensus that Westminster-style parliaments operate merely to rubber stamp, in partisan lock-step, the decisions of their cabinets has been called into question, especially in the UK. Lower levels of party cohesion on important votes (Rasmussen and McCormick, 1985), more frequent partisan defections among members of parliament (Norton, 1980), and accumulating evidence of a 'personal vote' in parliamentary elections (Cain et al., 1987; Norton and Wood, 1993) have led some scholars to examine influences other than party on the legislative behavior of MPs. This research has focused not only on backbench rebellions against the party whips, but also on free votes in the British House of Commons, unwhipped divisions on which party loyalty is not formally enforced (Moyser, 1979; Marsh and Chambers, 1981; Hibbing and Marsh, 1987; Marsh and Read, 1988; Pattie et al., 1994; Read et al., 1994).

Figures and Tables:
Table 1: Factor analysis of 15 votes on Bill C-43
Table 2: Full regression models of three vote groups on Bill C-43
Table 3: Reduced regression models of three vote groups on Bill C-43

Last Paragraph:
In conclusion, as in the UK, free votes in Canada do not result in many MPs abandoning their party majorities. Although a few do, they constitute a trickle rather than a flood. Parties are voluntary groups of like-minded people voting together, and the oft-decried 'bonds' of party unity are essentially self-imposed. Lifting the party whip, at least on the limited basis it has been done in Ottawa, reveals how strong Canadian partisan cohesion is, even on an issue as divisive as abortion.