A study by an Ottawa think tank has found that women remain underrepresented in boardrooms of Canadian companies listed on the Toronto Stock Exchange, despite the 2015 introduction of disclosure requirements intended to boost their numbers.

The Conference Board of Canada says that while there is some progress in the proportion of women on corporate boards, the pace of change remains slow.

The nonprofit's study found that women only made up 15 per cent of Canadian boards in 2018 -- an increase of just four percentage points from 2015, when seven provinces and two territories introduced so-called comply or explain requirements.

The Conference Board study says the rules that ask publicly traded companies to disclose the number of women in key positions or explain why they have not met their goals have failed to accelerate women's entry into boardrooms since they were introduced.

The study found more than half of the board seats that became vacant in 2018 went to men and about a quarter were left unfilled or eliminated.

The research was done by compiling all public disclosure reporting data released by the Canadian Securities Administrators from 2015 to 2018, which included data from 589 companies.