The authors imply that Liberal gradually declined as minority and catholic voters everywhere slowly left the party. However, had the authors of the study tied their musings to shifting regional voting patterns they would have come to different conclusions.
In 2004 Liberals share of the popular vote went up almost everywhere. It was up in BC, Alberta, Sask, Manitoba, NB, NS, PEI, NFLD. However, the party took a massive hit in Ontario and Quebec and lost its majority as a result.
Now, what happened in the former was Ontario voters returned to the NDP after an 11 year hiatus. Between 1965 and 1993 the NDP vote in Ontario never diped below 19% and never topped 22%. The party's share of the vote was very predictable. However in 1993 the NDP took only 6% of the the vote and their share of the vote stayed low for the next two elections. They took 10% in 1997 and 8% in 2000. Then in 2004 they went up to 18%. They took 19.5 in 2006 and 18% in 2008. As Ontario has by far and away most visible minorities in absolute terms, an 10% NDP uptake in the Ontario coupled with a 6.8% Liberal downturn in the province could mean that what is passed off as the start of a national trend (i.e., Liberal minority voters leaving the party) was really no more a province returning to traditional voting patterns.
Of course, that is not the only thing wrong with the implication that Liberals lost as minorities everywhere deserted the party. The Liberal share of the national vote went down 6.5% in 2006, but the Liberal share of the minority vote went up slightly.
Equally problematic is the implication that the party lost as Catholics abandoned the party. The problem is this. One can not seriously address the decline in the Liberal share of the Catholic vote without commenting on declining Liberal fortunes in Quebec, but that is what the authors do. As of 2001, 83% of Quebecers referred to themselves as Catholics. The next highest was NB at 54%. Outside of Montreal the number is much higher. Only 74% of Montrealers identified themselves as being Catholic. By comparison Quebec City is around 95%. Anyway, between 2000 and 2006 the Liberal share of the popular vote in Quebec fell 24%. Outside of Montreal the decline was even more dramatic. In the aforementioned Quebec City, for example, the Liberal vote was a third of what it was in 2000.