Women still earn about 10 per cent less than men after taking into account all measurable factors other than gender, new research has found.
The study found that only about 4 per cent of the average pay gap of about 14 per cent over recent years could be explained by gender differences. The "unexplained" gap of about 10 per cent would represent a woman earning $292,968 less than a man based on 10 per cent of the current male average wage of $31.30 an hour in a fulltime job at 40 hours a week for 45 years.
Authors Dr Gail Pacheco of AUT University and Dr Bill Cochrane of Waikato University said it was impossible to say whether the unexplained gap was due to bosses discriminating against women or other factors that they couldn't measure.
"We controlled for everything that we could control," Dr Pacheco said.
She said overseas research had found the pay gap between men and women was higher at higher incomes, partly because minimum wage laws forced more equal pay at low incomes while a "glass ceiling" often excluded women from top jobs.
"There is a common thing that women don't put their hand up [for pay rises], but there is also an element that it could be discrimination."
The study found that the gender gap in average hourly earnings narrowed from about 18 per cent in the early 1990s. The gap has widened again was 13.3 per cent at the end 2015.
Coalition for Equal Value Equal Pay economist Prue Hyman said the finding that about two-thirds of the gender pay gap was unexplained was higher than in many overseas studies.
But she said it might be partly because the study used only the broadest breakdown of industries and occupations.
NZ Initiative economist Dr Eric Crampton said the study did not look at pay differences between qualifications in different subjects.
E Tu union official John Ryall said a working party led by Governor-General-designate Dame Patsy Reddy was due to report to ministers on principles to be used by the Employment Court to determine cases such as a claim by caregiver Kristine Bartlett that she is underpaid because she works in a female-dominated industry.