I’ve always found prequels strange.

I presumed the main story began and ended where it did for a reason: that it captured the interesting bit. But the prequel asks us to believe that all the stuff before that – the very things that were originally deemed to be of insufficient consequence or fascination to form part of the story proper – was actually very interesting after all. Hence, the obvious objection: if it was so interesting, why leave it out in the first place?

Illustration: Andrew Dyson

But years of experience with endless prequels has now revealed their use. Having been inducted into a universe – and only after having been so inducted – we crave to know how that universe was formed. So it is that this week we discovered Centrelink is pausing debts currently being paid by 86,000 people. The reason is that those debts were calculated using a method called “income apportionment”, in a way that we now know was unlawful.

More on that shortly, but you’ll immediately hear the echo of robo-debt in all this, which used “income averaging” to determine whether people had been overpaid unemployment benefits, then used computers to generate debt notices automatically.

The trouble is that income averaging – which takes everything someone has earned over a year and presumes it was earned evenly across the year – is very often inaccurate. That’s especially true for people in casual work with irregular shifts, who might have lots of work in one month, then very little the next.

If you simply average this out over the year, the leaner months become invisible to you, and you begin to assume people received greater JobSeeker payments than they were entitled to. And when you use machines to chase them for money they didn’t actually owe, and couldn’t afford to pay, you can destroy their lives. The result was a string of broken lives, including suicides.

“Income apportionment” is a similar folly with a similar problem.

The basic idea was to take the income you earned in a payslip, and simply assume you earned the same amount every day over that period – to apportion it evenly. That’s fine if your payslip happens to cover the same fortnight Centrelink uses to calculate your JobSeeker payment. But if your payslip is out of sync with Centrelink’s fortnightly periods, problems arise.