Covid by numbers: How to beat the odds and use simple maths to stay safe
This maths whizz says we need to keep an eye on the statistics when making our decisions.
Navigating fast-changing circumstances has been the norm since the pandemic hit, and in recent weeks Australians have faced contradictory messaging around the AstraZeneca vaccine.
When Barbara Holland, professor of mathematics at the University of Tasmania, was making the decision to have an AZ jab now rather than wait for Pfizer, she deployed her number-crunching prowess.
Holland is 45 and well under the Australian Technical Advisory Group on Immunisation’s latest recommended age for AZ (60+).
She turned up at the vaccination hub in Kingston, outside Hobart, at the end of the day to ask if they had any AZ spare. “They said, ‘We’ve had three no-shows, you know the risks, so feel free to get one if you want’.”
The New Zealand-born mathematician had done her sums.
“If there’s any silver lining to a pandemic, it has made people realise the importance of mathematical modelling, such as the tools that epidemiologists use,” she says.
Using UK data, she calculated that “I’d have about a 1/60,000 chance of dying of Covid-19 in the next 90 days; balance that against a 1/900,000 chance of a fatal blood clot, working off a 1/30,000 chance of a clot x 1/30 chance of it being fatal.”
In that case, Holland reasoned, “even disregarding any community benefit of getting a vaccine, and just thinking about self-interest and the lowest probability of dying, if I were in the UK I would definitely get the vaccine”. Based on Australia’s numbers since the initial outbreak, she calculated that her risk of catching Covid-19 and dying was about one in a million. The risk of the Delta variant “getting away” and the community benefit of being vaccinated tipped her decision (which she stresses was a personal choice) to get the jab now.
Next month, Holland will discuss this in her talk, Using Maths to Make Rational Decisions in an Uncertain World, at Tasmania’s Beaker Street Festival – billed as “a celebration of science, art, and curious minds”.
“I have a statistician’s way of seeing the world,” she says. “Where is the data from? Is it really representative? Were there any confounding variables? Are you applying cause and effect? That’s all just second nature to me.” She suggests we should all remind ourselves of the underlying principles at play in common calculations.
“Such as, why you should never buy the extended warranty, but why you should always insure your house,” explains Holland.
“It’s the same mathematics: the people who sell the extended warranty have a good idea of the probability of a breakdown, so they’ll set the price so they’re guaranteed to make money, on average. The insurer who sells you insurance for a house does the same. When you buy insurance, you’re controlling the worst outcome: if you don’t buy the extended warranty and your toaster breaks, you can probably afford to replace it, but if you don’t insure your house and it burns down, that’s a pretty big problem.”
If the worst outcome wouldn’t be financially ruinous, ditch the insurance.
Booking holidays is a hot Covid dilemma and Holland says this is where decision theory comes in.
“One strategy is to be an optimist: ‘If I book a holiday, the best thing that can happen is I’ll get to go on holiday.’ A pessimist will think, ‘If I book a holiday and there’s an outbreak, it will get cancelled and I’ll lose money and spend hours on the phone to travel agents’.”
She concedes that it is a tricky calculation.
“Put weight on ‘how upset I’ll be if I make a booking and lose it’, versus ‘how happy I’ll be with my holiday’. Try to solve it as a maths equation.”
Holland puts herself in the pessimist camp, yet she booked to go and see her family in New Zealand and successfully ran the gauntlet of the trans-Tasman travel bubble.
The tip is to be alive to the opportunity of applying a mathematical mindset in making these decisions.
In collaboration with the UTAS philosophy department, Holland teaches a class in Good Thinking: Reasoning skills for life.
“In a fairly maths-free way for humanities students, we chip in with common tricks and traps and numerical reasoning,” she says.
“You don’t need heaps of maths to get your head around the important statistical ideas. A cartoon sums it up: “Hands up if you enjoy responding to surveys, or hands up if you can’t be bothered. Look! 100 per cent of people enjoy responding to surveys! Many things draw from a very biased sample, and once you think about it you see it all over the place.”
Holland notes that the insurance and gambling worlds use similar kinds of calculations, and that “the house always wins”. Even so, David Walsh famously funded his MONA museum in Hobart from gambling profits.
“We were on a session together at the Beaker Street Festival a couple years ago, and that was fun,” says Holland.
“David says, ‘People say that I’m brilliant and I outsmarted the system, but have I, or is it survivorship bias? Maybe there are a million ghosts of me out there that had gambling schemes that didn’t work, and therefore you’ve never heard of them!’ But I suspect he’s doing himself a disservice.”
The Beaker Street Festival runs in various locations around Tasmania from August 6-14. www.beakerstreet.com.au
