But as Rebekha Sharkie proved in Mayo in 2016, upsets do happen. The Coalition’s decision not to run in the two West Australian seats limits the potential federal implications that can be drawn from there. However, there could be one leader whose future is tied to the WA results: The Greens’ Richard Di Natale. The Greens have taken an increasing share of inner-city voters off Labor in recent decades and Perth and Fremantle are no different.

That vote will naturally jump this time with the Coalition not running a candidate. But after a worse-than-expected performance at the Batman byelection in March, Di Natale will be hoping for a strong showing this time around. Perth is not exactly Greens heartland, and the party would not be expected to win either seat, but if they fail to generate any momentum it might increase pressure on Di Natale. Lesson 1: Look to Perth and Fremantle to check the Greens' progress heading into the next federal poll. While we’re on minor parties The big political trend of the past 30 years has been the drift of first-preference votes away from both major parties.

However, because of the preferential voting system, they have still largely maintained their stranglehold on the House of Representatives. In 2013, Mayo was one seat that took the leap to a minor party, Nick Xenophon Team. It has not been a smooth road, with Xenophon’s departure for state politics backfiring, and forcing the party to rebadge. Sharkie, however, seems to have retained a high level of support. The Mayo byelection, then, shapes up as a referendum on the merits of minor party representation. If the Liberals can’t wrest it back into the fold, both major parties will be concerned that other previously safe electorates might start seriously considering alternatives. Lesson 2: Mayo could indicate what threat minor parties pose at the next federal poll.

Turnbull vs Shorten That leaves just two seats, Braddon and Longman, to be fought out between the Coalition and Labor. A frequently used line of this campaign is that no government has won a seat from the opposition at a byelection since 1920. While true, this masks the reality that relatively few seats change hands at byelections at all. There have been 152 byelections since Federation, and only 35 (23 per cent) of those seats changed hands. There’s a reason for that. Most byelections happen in safe seats.

As Stephen Barber noted in a Parliamentary Library research paper in 2014, “Political parties and individual members are only too aware of the possible political consequences of losing a seat at a byelection, and thus try to ensure that byelections caused by resignation occur only in relatively safe seats.” This has meant that of the 63 byelections caused by resignations since 1949, only 12 (19 per cent) have been in a seat on a margin of less than 6 per cent. The difference here is that Labor had no choice in resigning the seats after their 2016 candidates were deemed ineligible for citizenship reasons. Braddon is on a tight margin of 2.2 per cent, and Longman a wafer-thin 0.8 per cent. Meanwhile, oppositions have lost two seats at byelections this century, just not to the government. Labor lost Cunningham to the Greens in 2002, and the Coalition lost Lyne to independent Rob Oakeshott in 2008.

There is no likely minor party winner in either of these seats, but there definitely has been swings away from oppositions before. Lesson 3: Don’t believe it’s all upside for the government. The pendulum effect All five seats swung away from the government in 2016 on a two-party basis. The size of the swing is highly relevant, especially when considered against the sitting MP's current margin.

If even half the voters who switched sides in Braddon in 2016 decide to go back to the government, Labor will lose the seat. In Longman, if just one in nine of those swinging voters change their mind the seat falls. Longman also recorded an unusually high percentage of informal votes at the last election - 8.5 per cent - so if any party can woo those votes back into the mix they will do well. Then there’s the One Nation factor. Labor only won Longman in 2016 off the back of One Nation preferences.

Pauline Hanson (and her mouthpiece Mark Latham) have been vocal in their criticism of Labor this time around. But One Nation voters are fairly headstrong, and will likely make up their own minds as to whom to place second. Lesson 4: Both sides will keenly watch the flow of preferences from One Nation to strategise how to engage with the minor party from here. How representative are the five seats? If you're going to try to extract meaning from the byelection results, it helps to know how representative these seats are of the rest of the country.

The five electorates are very different. The two WA seats are relatively wealthy, well-educated and multicultural. The others are not. In fact, Braddon is one of the poorest, least educated and least multicultural electorates in the country. So when looking at byelection results from Braddon and Longman it’s best not to assume this is a gauge of how the leaders are doing with the overall country, rather with a particular segment of Australia. That said, Labor’s number one attack on the government has been that they govern for big business and the wealthy at the expense of "working" Australians. If those messages fail to resonate in Braddon and Longman of all places, then Labor’s strategy - and by that rationale Shorten - is in serious trouble.