The percentage of spin

Now with the numbers of COVID-19 cases in Australia well over 5,300, and despite the rate of growth of recorded cases starting to ease off, the number of new cases is still at about 200+ per day1. So, what does Morrison do? Her refers to the rate of increase in percentage terms, stating that it now is in ‘single digits’ on a percentage basis2. This is lying by misleading or dissembling3. It is designed to make the figures appear better for him among those who do not understand how this spin works.

If the number of new cases was constant at about 200 for several months, then the percentage rate would constantly decrease over time as the total number of cases increases while the added daily cases remains at 200. For example, if there were 1,000 cases, an increase of 200 is a 20% increase, while if there were 5000 cases an increase of 200 is a 4% increase. The number of new cases is constant, but in Morrison’s spin, it would appear to be improving dramatically. A more useful and less misleading description is the doubling time. This is the time it takes at the current rate of increase for the number of cases to double. At the steepest part of the infection curve, the doubling time for Australia was about 3.5 days. For example, on the 20th of March, there were 847 recorded cases. Double that number of cases (1,694) was passed during the 24th of March (i.e. 3.5 days). Now, the slope of the curve is starting to decrease, such that the doubling rate is now about 12 days1.

For some other countries, the current doubling times are quite dire. The United States has a doubling time of about 4 days. Spain now is about 6 days, while Italy is now about 11 days1. However, these rates are dependent on the testing regime, which varies enormously from country to country, and may be missing asymptomatic or mild cases entirely. Therefore, there is a suspicion that many places across the world have under-reported the actual number of cases. This is because severe cases, which more likely lead to fatal outcomes, are more often detected than mild or asymptomatic cases, and the reported death rates are therefore probably inflated in most countries.

A recent study utilises a benchmark country, South Korea, and its reported death rates, where testing has been extensive, in combination with population demographics to correct the reported COVID-19 case numbers elsewhere. By applying such a correction, it was predicted that the number of cases is very much under-reported in most countries. In the case of China, it is estimated that more than 700,000 cases of COVID-19 actually occurred instead of the confirmed 80,932 cases as of March 13, 20204.

Another recent study has estimated that, in Italy when the reported count was 1128 confirmed cases, this comprised only 28% of cases, with 72% going unreported. The true outbreak size was therefore estimated to be 3971 cases (with a 95% confidence interval of between 2907 to 5297 cases)5.

Up until recently, testing in Australia has been targeted at people who have travelled, and those connected to them, or people connected to those who have tested positive. Prime Minister Scott Morrison has stated that the Australian rate of testing of 10,000 per million, and said “We are the first country to the best of our knowledge that has been able to exceed that mark”6. That is either a lie, or Morrison didn’t look very far. I suspect it was the former. Iceland has tested almost three times that rate, last time I looked (28,000 per million). That is how they knew that a large proportion of those who tested positive were asymptomatic7. They have now offered free coronavirus tests to all citizens8. Bahrain has tested over 20,000 people per million9, twice the rate of Australia, and Germany has also tested more than Australia, at about 11,000 per million10.

To get an understanding of how many actual cases there are in Australia, and how significant is community transmission, we need to go to random testing. Next Monday, April 6, the government of the Australian Capital Territory will begin actively searching for these, allowing a random sample of previously ineligible people to be tested. This is in part because the number of travellers remaining to be tested, is decreasing11.



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