The size of Australia’s gender pay gap has been stable for 20 years, but the reasons behind it are changing.

A new report by analysts at KPMG says Australia’s 16.2 per cent gender gap in wages is kept open by discrimination against women, with other factors including skills, experience, education level and tenure all decreasing in their influence on the pay gap.

Part-time employment contributes to the gap, as women are overrepresented in that style of work, but the influence of part-time work has decreased from 14 per cent in 2009 to four per cent in 2016.

KPMG says the idea of ‘traditional roles’ in the workplace now accounts for almost one third of the gap

Additionally, women are being set back even further if they decide to take time off work, with the proportion of the gap attributable to years out of the workforce increasing from 9 per cent to 21 per cent.

“What we're talking about here is much more sinister … It's the unconscious biases and the systemic market issues — that women are almost trained from birth, shall we say, to fall into those traditional caring roles,” said the report author, Tamara Price.

“Then you wind up in industries that are systemically paid less than the industries that have men in them.”

KPMG partner Susan Ferrier says there has been a change in attitude towards the issue of pay equality, but it is not reflected in the numbers.

“I've seen a real shift in the global conversations, but bringing it closer to home, a real shift in the conversation in Australia — particularly at the senior executive level where it's seen as a critical business issue as opposed to an issue that's being managed off to the side somewhere deep in the organisation,” she said.

Sex Discrimination Commissioner Kate Jenkins said the gender pay gap was depriving women of economic security.

“I am particularly disturbed by the finding that sex discrimination remains a persistent feature of the workforce, and one component that is actually increasing,” she said.

“Women, families and our economies pay the price in the long term for these underlying social attitudes towards women.”