The Federal Treasurer, Joe Hockey, recently caused a storm by suggesting, among other things, that if Sydney housing was unaffordable no one would be buying it.

People are indeed still buying housing, even first home buyers, but the way they are purchasing has changed.

The past three years have seen the rise of the first time home buyer investor.

A survey by Digital Finance Analytics shows that the proportion of first home buyers purchasing as an investor went from less than 5 per cent in April 2012 to 35 per cent by April 2015.

In Sydney, investors accounted for almost 60 per cent of first time buyers.

One of those first time buyer investors is 26-year-old Caitlyn Black.

"I was very keen on getting into the property market, but to afford somewhere in this area was going to be nearly impossible, so I decided to look further out and purchase as an investment property," she said.

Caitlyn rents an apartment close to her work in the Melbourne CBD, but rents out a property thirty kilometres from the city centre.

"There are a couple of auctions that have occurred in the street that I live in and they're well beyond the budget that's for sure," she added.

There are a multitude of factors which influence affordability and prevent Caitlyn owning something nearer to where she works, and the major determinants vary depending on who you speak to.

"Affordability's one of those things that's extremely tough to measure because it's different for everyone," answered CoreLogic RP Data real estate analyst Cameron Kusher.

People are buying houses, but more and more of them are investors for whom housing is more affordable than owner occupiers.

Negative gearing tilts the equation in favour of investors as they enjoy the tax benefits through the life of the asset.

Of course, affordability is not even an issue for many.

"I think affordability is one of those things that affects those people that don't currently own a home or have only recently purchased a home," added Mr Kusher.

Urban planning lobby group Demographia ignores interest rates when considering affordability because they vary over the term of a mortgage.

It essentially looks at the ratio of median disposable income to median house prices.

A ratio of three times disposable income and under is affordable with 5.1 and over considered severely unaffordable.

'A nationwide crisis'

Australia and New Zealand are in a class of their own, countries with the least affordable housing in the developed world, but it all depends on how you measure median house prices and incomes, which differs from country to country.

Nevertheless, it is an outcome that rings true to many who say the affordability crisis is not restricted to Sydney and Melbourne.

Professor Andrew Beer, the director of the Centre for Housing and Regional Planning at the University of Adelaide, said it is "a nationwide crisis".

"Often while house prices are greatest in the big cities, even in regional Australia many people can't afford housing because while their house prices might be lower their incomes are lower too," he explained.

Mr Kusher said it is a lack of homes on the market that is contributing to some of the more extreme price rises.

"The sales that we're seeing now, they're still a long way from where they were back in 2000 and 2003 when we were getting about 45,000 house sales a month nationally," he observed.

"At the moment we're getting about 32,000 a month, and the population's increased by about 3.5 million over that time.

"So you would expect in an efficient, affordable market the number of sales taking place should trend higher over time. That's simply not happening."

Caitlyn would like nothing more than to afford a conveniently located home of her own.

"If it was within my budget and wasn't going to impact my lifestyle, but I think that is very far out of my reach at the moment," she said.

So she will bide her time as an investor instead.