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# Opinion Colm O'Regan crunches the Covid-19 numbers, and sums up isolation matters

When you look at virus modelling, staying at home now makes absolute sense, writes O’Regan.

IT’S A GRIM daily ritual. Waiting for the numbers of new cases. The increase is nearly always bigger now. There is a powerlessness associated with it.

For a small amount of, probably misguided, self-care I try to gain control of the numbers. Just to write them down in a list. There’s something you should know about me – I do like a spreadsheet, and since early March, I’ve been filling the numbers on corona dot xls.

Friday’s number was 683, an increase of 126, or 22%. Thursday’s increase of 191 was 52% higher than Wednesday. Those numbers don’t look too far apart. And percentages are only ‘bits of things’ aren’t they? But do a small experiment.

A little effort yields a lot

If you have a smartphone, open up the calculator. It might be located near other stuff you didn’t know ‘this yoke could do’, like the compass, the four-inch ruler or the mirror. Don’t get distracted by your reflection, just open the calculator. This is important.

Put in Friday’s total, 683. Pretend new daily cases arrive in from now on at that same rate. Multiply it by 1.22 as a guess of what it might be today. Multiply the answer again by 1.22. Do that another six times. So by a week’s time, we could have 2,748 cases if we carried on at the same rate.

Now do the same but multiply 683 by 1.52, as if we had a week like Thursday’s numbers. Next Friday we’d be watching a press conference announcing the number 12,803. Ten and a half thousand cases is a big difference. The difference between properly socially isolating and acting the maggot.

This is the scary power of exponential growth. Which is how viruses grow before we get a grip on them. Like, literally, epic and legend, exponential is one of those words that has had its meaning diluted over the years. But exponential has come roaring back. You might have first seen exponentials in first-year maths in secondary school. A small number appearing above the x in algebra in Double Maths after lunch with the radiators and the winter sun putting you to sleep.

You’ll hear on the news that the virus is growing exponentially. It means a thing is growing over time at a rate that’s proportional to the size of the thing itself. The more people have it, the faster others will get it. You see exponential growth in the compound interest, in your savings account (if you’re lucky enough to have one) but the rate of growth is so tiny you might as well put it under your mattress. How we’d only love a virus that grew at a deposit rate right now.

Even if the virus grew at 22% a day, the ‘Friday’ rate, in my half-arsed spreadsheet, theoretically 100,000 of us would have it by the middle of April. Now, a basic spreadsheet is only useful for a very first guess of possible futures. A simplistic extrapolation.

Infectious disease modelling

Medical maths must be smarter than that. It uses mathematical models. A model is a set of very complicated equations that mimics the behaviour of a system in certain conditions. A system can be physical like the weather, biological like disease or social like crowds.

So for an epidemic, they are modelling what the virus does – how contagious, how it’s passed on – and how people behave. You would think people are hard to model because there’s nowt as queer as folk but mathematicians do a reasonable approximation. They look at age, location and also random chance encounters between people and a rake of other factors.

It’s a far advanced level of the maths we did in school but there is still a direct line from Folens New Complete Mathematics algebra to here. The last equations some of us might have done in school were simple: “What kind of a thing do we get if you square a thing, add four times the thing and add another fifteen?”. Whereas modelling of infectious diseases would be like solving our above equation in a strong wind, while someone was hitting you with a stick, and the other fella you were expecting got stuck in traffic in the Jack Lynch tunnel.

Bless the mathematicians

Models aren’t perfect. They can’t take into account the unknown – political, financial or behavioural. But they start us off. They gain the attention of politicians and eventually the wider public.

Ultimately it’s all about finding one important number. The virus’s basic reproductive number, R0 (R-zero), tells us how many other people you would infect if you had the coronavirus. With a number less than 1, the disease would die out eventually. If it was 1 the disease would carry but wouldn’t explode and if the RO was greater than 1 eventually the virus would spread and become an epidemic.

According to the models, the R0 for Covid-19 varies between 1.5 and 3.5. That’s if we do nothing. Call it the ‘Cheltenham option’. A lot of public health work aims to reduce R-zero to below 1 because then the virus would then die out. That’s what social distancing, physical distancing is for. And why queuing for the Blanch Krispy Kreme with the squad is a bad idea. But Ringsend Flats Bingo is a better one.

It all boils down to this. In this weird war with an invisible enemy, one that you can’t simply tell to ‘eff off’, we can feel like we are at the mercy of the numbers. But we are the most powerful agent in all of these models.

Look at your calculator again and that grim daily multiplier. The power to change it is in your hands (which you should wash).

Colm O’Regan is a comedian, author and broadcaster.

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Colm O'Regan