The NDP's Tom Mulcair is rated the most competent and trustworthy of the five candidates vying to be prime minister, while Conservative Leader Stephen Harper is the least trustworthy and competent, according to the latest results from Vote Compass, CBC's online voter engagement survey.

Green Party Leader Elizabeth May follows Mulcair most closely on the issue of trust, while Bloc Québécois Leader Gilles Duceppe comes second in competence.

The findings are based on 382,643 respondents who participated in Vote Compass between Aug. 29 and Sept. 20.

One of the reasons Harper ranks so low is that when the Vote Compass results are broken down by party preference, only Conservative voters give him high ratings, says Clifton van der Linden, founder and director of Vox Pop Labs, which developed Vote Compass.

By contrast, the other leaders received high ratings from their own voters as well as relatively decent ratings from supporters of the other parties.

"So that affects the way the averages turn out in the end," says van der Linden.

Vote Compass asked respondents to rate the trustworthiness and competence of the five party leaders on a scale of zero to 10 (where 10 is the most trustworthy or competent).

Overall, Mulcair averaged a rating of 5.1 on trust and 5.5 on competence, and May rated 5.0 and 4.4, respectively.

Liberal Leader Justin Trudeau rated 4.7 on trust and 4.5 on competence, while Duceppe rated 3.9 and 4.6.

Harper rated 2.9 on trust and 4.2 on competence.

The issue of leadership will be on full display as the five leaders head into the first French-language debate in Montreal tonight.

How to watch Thursday's debate

The French-language leaders' debate will be broadcast live and live streamed online 8 p.m. to 10 p.m. ET Thursday.

You can watch the debate in simultaneous English translation on CBC News Network and online at CBCNews.ca/Canada Votes beginning with a Power & Politics pre-debate special at 7 p.m. ET. The debate will be broadcast in French by Radio-Canada (check local listings) and live streamed online at ICI Radio-Canada.ca.

The debate is being produced by a partnership of Radio-Canada, La Presse, Télé-Québec, CBC News, CTV News and Global News, together with Facebook, Instagram, Twitter, Vine, Google, YouTube and CPAC.

'Unease with Harper'

Leadership appears to be a more prominent theme in this campaign than in the last federal vote in 2011, says Penny Collenette, an adjunct law professor at the University of Ottawa who worked in the Prime Minister's Office under Jean Chrétien.

That may be, at least in part, because the Harper campaign has emphasized that the prime minister has the experience and authority that his rivals lack, particularly when it comes to the economy and foreign threats.

But the Vote Compass results reflect "a real unease with Harper," says Collenette, and it seems to be across all categories, such as party preference, demographics and income.

She notes that polling data on incumbent leaders is often lower than for candidates who haven't faced the same tests of office. But she also feels that the numbers for Harper, who has been prime minister since 2006, "shouldn't be this low."

The Vote Compass data also offers some insights into the thinking of undecided voters, who may be wavering between a number of leaders, says Dennis Pilon, an associate professor of political science at York University in Toronto.

For example, on the issue of trustworthiness, Green Party supporters give Justin Trudeau the second-highest rating, after May. For Liberals, it's Mulcair. For BQ voters, May comes second.

On the issue of competence, the respondents seem even more conflicted.

Green Party supporters seem stuck between Trudeau and Mulcair as their second choice. Meanwhile, NDP supporters rank both May and Trudeau quite highly — as do Conservatives.

"Those splits reflect a tug of war in the hearts and minds of voters, who are still not quite sure," says Collenette.

Developed by a team of social and statistical scientists from Vox Pop Labs, Vote Compass is a civic engagement application offered in Canada exclusively by CBC News. The results above are based on 382,643 respondents who participated in Vote Compass between Aug. 29 and Sept. 20.

Unlike opinion polls, respondents to Vote Compass are not randomly selected. Similar to opinion polls, however, the data are a non-random sample from the population and have been weighted in order to approximate a representative sample. Vote Compass data have been weighted by geography, gender, age, educational attainment, occupation, religion, religiosity and civic engagement to ensure the sample's composition reflects that of the actual population of Canada according to census data and other population estimates.