At the time there was one woman on the executive team, but too few were coming up through the ranks equipped to step into leadership.
"Really, the findings were no different from what you might think they would be," says Brown.
"It was definitely things around the perception of what it is like to work in a senior role and how on earth do you do what I call a struggle with the juggle."
But what was an eye-opener for Brown was the persistent view that you still needed to be one of the boys to make it at the bank.
"We were really surprised it was still there in this era, in this generation - that we were still talking about the fact that there was the language, the activities that felt isolating for women."
She says the response was not just to work on diversity, but also to introduce a significant behavioural programme for the bank's leaders.
A lot of time was spent helping leaders understand who they were as a person, as a leader and what their purpose was, Brown says.
"When you come through the door, when you enter this business, you bring your whole self and your whole being, then you're going to be open to not playing this game or not being something that you think you need to be."
Brown says that when introducing diversity initiatives, she always backs them up with data on the business benefits of bringing more women into leadership positions.
In 2009, the Harvard Business Review noted that women consumers made up a potential growth market twice the size of China and India combined. Consumer research in the US showed that women made 80 per cent of purchasing decisions, while similar studies in Australia pointed to 90c in every household dollar being spent by women.
At a macroeconomic level, some economists have suggested that closing the gender pay gap would boost New Zealand's GDP by as much as 10 per cent.
At leadership level, companies with a decent representation of women in board and executive roles outperform their less diverse peers.
"And still to this day I have to go back to the 'why' on this and I've decided that that's never going to go away and I've actually stopped being frustrated now that still you have to talk about why women are needed."
The past five years have seen the bank introduce a programme identifying highly talented women who are provided with the training and support to move into leadership. Recruitment policies have been updated to require at least one woman on every shortlist.
But, says Brown, "it's not about putting a woman in for woman's sake; it's always about the best person for the role.
I constantly get asked that and it's not to say that every woman is the best person for the role - you've still got to run a business - but if we're not actually going out there and finding the fabulous women and encouraging them to come into our bank, then we're only half doing this job.
Once people are in the door the big issue is job flexibility, but Brown says her opening stance is that every role is flexible and it is a matter of working out what this entails.
Brown herself works most of the time in Wellington, despite her role officially being Auckland-based.
So what's changed in five years?
During exit interviews with senior women, the reasons for leaving have changed from dissatisfaction with their immediate boss, to today, when the main reason for moving on is to advance their careers.
To which Brown says "hallelujah!", before ensuring they stay connected to the bank should a future role come up.
Brown is in the process of re-doing the original study "because sometimes when you lift up the rock what you find is more of a wiggly old mess than you thought was actually there", but she already knows, on raw data alone, there's been an improvement.
She says working to improve diversity is relentless, but "we just started doing some stuff and what worked we kept going with, what didn't work we changed.
"It's like anything you do in business and it just has to be part of your business."
