Dan Andrews’ announcement of a slow, cautious return to normal left many Victorians frustrated. But the premier says he has no choice — modelling done for the health department by the University of Melbourne showed that if the state eased restrictions too soon, Victoria would have a 64% chance of being locked down again by Christmas.
“You can’t argue with this sort of data, you can’t argue with science, you can’t do anything but follow the best health advice, otherwise … we will just be beginning to lose control again of this virus,” Andrews said on Sunday.
But despite Andrews’ claims that the numbers don’t lie, there’s been plenty of criticism of both the modelling, and the lack of transparency around it.
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What do we know about the model?
The University of Melbourne team used what’s called an “agent-based” model. Agents, or people, move around like pieces on a chessboard. When a person enters another person’s square, they become infected with COVID-19. As restrictions are added or relaxed, the way they move around the chessboard changes.
The researchers used a supercomputer to run 1000 simulations of the chessboard, with variables put in place — factors like compliance with mask-wearing, observance of social distancing,
What we don’t know
The problem with Victoria’s reliance on a model to justify continuing restrictions is there’s a lot about the model we just don’t know, says Deakin University epidemiology chair Catherine Bennett.
“The model depends on the parameters you put in it, and this model appears to be built from info we knew earlier on from various settings around the world,” Bennett told Crikey.
Without seeing those parameters, we can’t get a firm picture of how good the modelling really is. Instead, there’s not been a huge amount of transparency around it, Bennett says.
“We don’t know what questions were asked of the modellers by the government, or what they tested,” she siad. “We don’t know if they’ve updated the parameters. We don’t know what the scenario for opening up was.”
Andrews’ big claim — that there’s a 64% chance of returning to lockdown if restrictions are eased to soon — is a case in point. The modelling doesn’t tell us whether that’s in a scenario where there are no restrictions at all, or whether even if some restrictions are in place a return to lockdown is likely.
The modelling also doesn’t account for different rates of transmission in certain areas, like aged-care settings and among health care workers.
Speaking to ABC Radio National Breakfast yesterday, Doherty Institute director of epidemiology Jodie McVernon also said the modelling provided “scant” detail.
“There was very little detail of the modelling that was presented yesterday and I think it was probably disappointing that we didn’t hear more of a description of what the locations of infections were,” McVernon said.
Does it matter?
Modelling isn’t a magic bullet to save Victoria but should just be one element underpinning a policy decision, according to Flinders University professor of medicine Nikolai Petrovsky.
“A model is useful, but should never be what determines your policy. Real world evidence, what happens in other countries, all should be considered,” he said.
Petrovsky said the toughest question facing Victoria right now wasn’t about the strength of the modelling, which clearly showed how distancing could lower case numbers, but whether a longer lockdown was the best way to deal with the current situation.
UNSW epidemiology Professor Mary-Louise McLaws says while the Melbourne University modelling seemed thorough, what mattered was that it had helped guide the Victorian government towards an approach she says is the right one.
“Modelling is a helpful element, that experts use to make a decision — a model doesn’t make the decision, it just helps,” McLaws said
“Hearing that they’ve done over 1000 iterations with several scenarios, knowing the limitations of models, I think they’ve done a very thorough job.”
With case numbers over the last two weeks falling but still high, McLaws said the critical issue was maintaining the cautious, conservative easing of restrictions necessary to beat the second wave.
“The critics have failed to understand that it’s the decision that matters.”
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