But some companies such as Westpac have achieved equal diversity in leadership roles, along with Genesis Energy, and Air New Zealand who have achieved 40 per cent.
"The point around leadership is that it's about equal rights and equal opportunities for both men and women," Burdon said.
"Unfortunately there's no silver bullet. The most tangible impacts come from clear accountability and transparency so there is an explicit commitment and target that people are held to, but underpinning that, if we're going to make a real change, has to be driven by changes in the culture of the organisation."
Enabling flexible work environments and increases to paid parental leave had proven to enable greater gender equality in leadership, overseas, Burdon said.
But Super Diverse Women founder Mai Chen said diversity, not only more women, is needed to better improve business performance.
"I think we just need to focus on difference. The trouble with diversity is that it has all become about women but actually everybody has a gender and ethnicity - I think what we need to focus on is being inclusive," Chen said.
"None of us want to be stereotyped ... we just want to be treated on merit."
Chen said businesses needed to broaden their scope to include not only more women but people of different ethnicities, backgrounds and LGBT.
"This is about diversity and inclusion. Diversity is about difference, we're all really different and so we just need to make sure that we are providing opportunities equally, particularly for people who have a range of characteristics, which sometimes are not appreciated in business."
The point around leadership is that it's about equal rights and equal opportunities for both men and women.
Businesses would lose customers and clients if they continued to focus on a narrow definition of diversity, she said.
"What customers want is to see themselves reflected in the businesses they use."
Air New Zealand chief people officer Jodie King said the current number of women in leadership roles was embarrassing.
"Corporates need to set some targets around women representation in senior leadership roles and think about whether their current leadership has any unconscious bias," King said. "There's a lot of work on hygiene factors that needs to be done such as maternity pay and corporates have got to be more open and accepting to different ways of working, and the benefits that can bring."