More than any other time in my career as a data journalist, the general public is obsessed with numbers. The number of coronavirus cases, the number of coronavirus deaths, the number of tests administered – as well as any analysis that slices and dices these data, whether that’s daily increases or per-person rates. The crucial problem is that, while everyone is saying that the total number of global coronavirus cases currently stands at 435,006, we actually don’t know this basic number. What we do know is the total number of confirmed global coronavirus (435,006). The real total is likely to be far higher, perhaps by as much as a factor of 20 in some countries. It would only be known if every single country tested every single one of their citizens with a test that was 100 per cent accurate. Below, we talk to the experts on the issues with the data that we all, rightly, are examining on a day-to-day basis. Testing inconsistencies may mislead the public The way we know if a country has a coronavirus case is if an individual is tested and a laboratory confirms a diagnosis of COVID-19. This might sound an obvious point, but it has huge implications for a country's recorded cases and death rate. A country’s case fatality rate will look a lot worse if there are no active steps to test for coronavirus in the community. States such as Germany and South Korea stepped up testing much faster than the UK, which is only testing those people who are in hospital. This means that the vast majority of UK cases are not tracked and, as a result, our fatality rate will look high. While Germany’s case fatality rate is 0.5 per cent, the UK’s currently stands at 5.2 per cent. Experts say that, because of the differences in testing policies between the countries, this is to be expected and does not necessarily mean that German doctors are better at treating the disease. Germany may also not have been recording all deaths from the outset, other experts warn. Research from Timothy W Russell at the Centre for Mathematical Modelling of Infectious Diseases indicates that as few as six per cent of cases – just one in twenty – are being recorded in the UK. Germany is estimated to be recording 69 per cent of their cases – over two thirds. This is because, despite promises of the UK getting up to a daily count of 25,000 tests, the maximum number of tests performed in one day stands at 8,400 on Thursday 19 March. Since then the average daily figure for testing has been around 4,500.

To work out the death rate, we are currently dividing 422 deaths by the confirmed number of 8,077 cases instead of a suspected number of cases which could be as high as 135,000. Compared to a death rate of 5.2 per cent, this research hints that it is more likely to be around 0.3 per cent. Prof Rosalind Smyth, Director and Professor of Child Health, UCL Great Ormond Street Institute of Child Health, warned that Britain simply has no idea how many cases it has because of a lack of testing. “On conservative estimates, the true figure is likely to be five to 10 times higher. It may heighten concern as people think the case fatality rate is much higher than it is, or provide false reassurance that the number of ‘cases’ in a given area is much lower than it is.” Unknown recovery numbers coming in two weeks time The UK currently defines “recovery” as being discharged from NHS care, two weeks after having returned a positive coronavirus test. This does not include anyone who self-quarantines with coronavirus symptoms and recovers on their own, meaning that – once again – recovery rate statistics will be lower than the real number because they do not include milder cases who stay at home. The latest Public Health England data show that 135 patients have recovered from a total 8,077 UK cases.

That would hint at a recovery rate of just 1.7 per cent, compared to China’s 90.1 per cent, South Korea’s 38.8 per cent or even Italy’s 11.6 per cent (according to data from the Johns Hopkins University). Once again, such data would seem alarming at first glance. But, once again, there are two caveats here. Firstly, as mentioned above, anyone who self-quarantines and recovers at home – which looks set to be the majority of UK coronavirus cases – will not be included in the total number of recovered cases. They will not be tested or recorded in any way by the UK authorities. Already the recovery rate statistics is lower than the reality. Another issue is the fact that there is a lag when it comes to recording recoveries. Early estimates suggest patients recover around 10 days after first falling ill, so it will still be another couple of weeks before the UK’s recovery rate begins to increase.

The reason Italy’s recovery rate is currently around five times higher than the UK is “almost entirely down to the fact that the exponential phase of the outbreak in Italy kicked off about a week or two earlier,” according to Professor Paul Hunter, Professor in Medicine at UEA. Taking care when comparing older countries to younger ones Another crucial issue is, due to the fact that coronavirus is affecting diverse countries with different demographics and political systems, data is inconsistent and should be interpreted with great caution. Italy’s death rate is far higher than China’s, for example. On the face of it, that might point to mismanagement of the crisis. But in Italy, over a fifth of people are aged over 65 with a median age of 45.8 years. On the other hand, just 11 per cent of China is aged over 65, with a median age of 37.7.

In tackling a disease which hits the oldest hardest, this demographic profile would give China an advantage. Therefore, experts warn that a crude comparison of death rates across the two countries is problematic. It is also important to factor in the proportion of a population with underlying conditions. Obesity is one proxy for this and on this measure the UK and US are among the most vulnerable in the world. Varying definitions of coronavirus death You’d imagine deaths would be pretty unambiguous as a measurement. They’re certainly a better indicator than infections, as they’re less dependent on testing. But experts warn that there is little international consensus on defining a “coronavirus death”. For example, Italy classes every patient who dies while carrying the coronavirus as being a death caused by the virus, potentially inflating the death toll. Prof Walter Ricciardi, scientific adviser to Italy’s minister of health, told The Telegraph: “The way in which we code deaths in our country is very generous in the sense that all the people who die in hospitals with the coronavirus are deemed to be dying of the coronavirus. “On re-evaluation by the National Institute of Health, only 12 per cent of death certificates have shown a direct causality from coronavirus, while 88 per cent of patients who have died have at least one pre-morbidity – many had two or three”. This would potentially adjust Italy’s 9.5 per cent fatality rate – an international outlier – down to 1.1 per cent of deaths caused directly by the virus, in line with current data from countries such as Canada and Portugal. Equally, however, you could argue that other countries might be downplaying the role that coronavirus played in deaths. Right now, without adequate research, it is hard to say the degree to which the disease is playing in the deaths of people with complex medical histories. Cause of death will become an increasing problem as health services are overwhelmed with new coronavirus cases.