Andrew Dyson In Tasmania, the smallest state, there are just over 30,000 people for each federal seat (when senators and lower house members elected in the 2016 are combined). That compares with 131,000 people per federal MP in NSW and 125,000 in Victoria. Queensland is the only other state with an above average population-to-federal-seat ratio. South Australia, Northern Territory and Tasmania were all well below the national average.

The population-per-seat in federal parliament varies widely between the states. Credit:Nicole Emanuel Of course, the authors of the constitution created an electoral skew in order to "protect" the smaller states. The constitution stipulates that each "original" state must have an equal number of senators, regardless of population. The current quota is twelve senators per state and two senators for each of the territories. The constitution also dictates that each state will have "five members at least" in the House of Representatives. Those protections for smaller states were part of the deal that transformed Australia's six colonies into a Commonwealth back in 1901.

But since then patterns of population growth have been very uneven. In 1901, Tasmania accounted for nearly 5 per cent of the national population. But the latest population estimates, based on last year's national census, show that share has now shrunk to just 2.1 per cent. When Australia's very first census was taken soon after federation, the most populous state, NSW, had eight times more people than Tasmania. But that multiple has now blown out to 15 times. A population comparison between Victoria and Tasmania since federation tells a similar story. On current trends, the population gap between Australia's biggest and smallest states will keep growing, making the state-based disparity in voting power even more pronounced.

Tasmania will soon be home to less than one in 50 Australians but it will continue to return almost one in six Australian senators. And Tasmania is not the only state with a shrinking population share. Since federation, South Australia's proportion of the national population has fallen from almost 10 per cent to just over 7 per cent. NSW's share of national population has also declined from 36 per cent of the national total to about 32 per cent since 1901. But it still has the least favourable federal-seat-to-population ratio due to its sheer size. A comparison of the federal representation enjoyed by a Tasmanian voter to that of a voter living in the outer suburbs of Sydney or Melbourne illustrates the arbitrary distribution of national voting power. Two neighbouring council areas in Sydney's west - Blacktown and Fairfield - together have a bigger population than the whole of Tasmania.

Likewise, in Melbourne's east the neighbouring council areas of Casey, Knox and Greater Dandenong together have a bigger population than Tasmania. But unlike their Tasmanian counterparts, those outer suburban voters in Melbourne and Sydney don't have 12 senators to represent them. The relative size of lower house electorates also contributes to the inferior population-to-federal-seat ratio in large states. Federal seats in the suburbs of Sydney and Melbourne typically have about 110,000 voters. But each Tasmanian electorate only has about 74,000 voters. The difference is due to that constitutional rule giving each state a minimum five lower house seats. At the last election the federal electorate of Canberra in the ACT had over 143,000 voters – almost double the number of electors for the seat of Braddon in north western Tasmania.

Rawnsley, who is a regional economics expert with consultancy SGS Economics & Planning, predicts that over the next 20 years "the NSW and Victoria population will continue to grow, but their impact on the federal parliament will continue to weaken". He reckons the rules that gradually reduce the potency of votes in big states are as obsolete as the citizenship provisions in section 44 of the constitution that triggered the dual nationality crisis that has embroiled a bevy of MPs including deputy Prime Minister Barnaby Joyce. "Sure section 44 is out of date but maybe first we should look at why a voter in Tasmania has 4.25 times more power than a NSW voter," he says. "As smaller states have a greater impact on the parliament you might see regional issues coming into conflict with the national good." But reform would require a constitutional referendum that wins majority support in every state. And voters in smaller states are very unlikely to agree to any change that crimped their political influence. So far, Australia's biggest states have quietly accepted their deteriorating share of federal representation.

But over time, the voting disparities driven by demographic change could undermine good policy and put pressure on the federation. The two smallest states already receive a disproportionate share of the GST which the Commonwealth splits between the states. Political tensions are bound to rise if some voters begin to feel they don't have a fair say. Matt Wade is economics writer. Ross Gittins is on leave.