The population debate involves three standard ways of presenting figures in misleading ways. No matter what your views are on the need for sustainable population levels, it’s helpful if discussions are based on accurate information.

Let’s be clear here: there is no 2050 population target; natural growth rates are different to birth rate; net migration rates are different to permanent migration rates.

You’ll hear the Liberal spokesman on immigration say the government has a target to reach 36 million people by 2050. Interestingly you won’t hear anyone from the government say the same thing. The reason is simple. There is no government 2050 population target.

The confusion on this came after the release of the Intergenerational Report. It was the third report of its type. The previous two had been under the previous government. It involved a projection of what would happen to Australia’s population if the next 40 years looked similar to the past 40 years.

So it included the rates of people settling in Australia, the increasing birth rate, increasing life expectancy and the rate of people leaving Australia. It came out with a projection that if recent trends continue, our population would be 36 million by 2050.

It was a projection. Not a target, not an ambition, not a policy.

That won’t stop the Liberal Party from claiming it’s all of the above, but it’s important as a starting point to know that neither side of politics has an arbitrary target for what our population should be in 2050.

The issue of natural growth rates versus birth rates is tricky but really important. National and state-by-state data will often compare the natural growth rate with the net migration figures. You end up with figures that, depending on where you are in Australia, say natural growth is about 30%-40% of population growth and net migration is the rest.

Then have a look at the way the ABS calculates population growth on its population calculator page. There the ABS adds a person to the population by birth every one minute and 46 seconds and adds a person by migration at the exact same rate. How can both be true?

Natural growth is births minus deaths. Net migration is immigrants (for more than a year) minus Australians moving overseas.

Grouping the figures this way carries a presumption that immigrants never die. Only people who are born here die and they never move overseas.

So when people talk about how many are added to our population through birth, it’s important they use the birth rate, not the natural growth rate if the information is going to be accurate.

Scott Morrison got his own party into much trouble talking about net migration against permanent migration. Each year in the Budget the government announces how many places will be available under the different categories of permanent migration. That provides the best guide of how many people are settling permanently in Australia. It was 182,450 in the last Budget.

The net migration figure can be interesting but it includes so many variables it becomes a pretty dodgy guide to any informed discussion on population. It counts how many people come to Australia for more than a year minus how many leave.

It includes a very large number of temporary visa holders. These visas are demand-driven and were established that way under the previous government. When our educational institutions can make more money from overseas students the numbers go up. When local skills shortages need to be filled from temporary visa holders, the numbers go up.

And when the visas expire for either of these categories, the visa holders go home. They can only stay permanently if they can fit within the permanent places, which are fixed in the Budget each year.  That’s why the permanent migration system provides the best guide.

There was a change in the methodology in 2006. The net figure before then only counted people who had stayed continuously in Australia for 12 months. This knocked out a lot of overseas students who would return home for a few weeks over summer. The new way of counting includes anyone who stays for 12 of the last 16 months, which means we now count a lot more students and backpackers within the net figure. So it’s impossible to compare like with like for more than four years.

There was also an unusual phenomenon during the global recession where fewer Australians moved overseas to find work and a significant number of ex-pats returned home. That movement also forms part of the net migration figure but it’s a bit much to use Australians returning home as part of an argument about immigration and population policies.

Sorry this is horribly detailed and all about statistics.

But if we are going to have a reasoned debate on how population impacts on growth, jobs, infrastructure and the environment, it’s important to clarify exactly what the base statistics mean.