I generally consider Reuters a valuable source of information. However a combination of 2 recent articles about Covid19 in China reveals Reuters interpretation of data is somehow naive. Data analysis led me to some China conspiracy hypothesis outlined at the end of this post, but let us see source data first:

April 23 Three negatives and a positive: problems with coronavirus tests in China

• Trader He Ximing from Wuhan caught the coronavirus
• X-rays showed his lungs had white blotches, similar to those found in coronavirus patients, but his nucleic acid test was not positive so a hospital declined to admit him.
• As a precaution, a committee that manages his housing compound put him in quarantine for 14 days.
• on March 28, he took a fourth nucleic acid test, which was again negative, but he was also tested for antibodies and got confirmation
• A survey by Chinese doctors in February looking at samples from 213 patients suggested a false-negative rate of about 30%.

Antibodies presence typically means one was infected and build resilience to the virus. Infection may be symptoms free. Article focuses on individual calamity of trader, but ignores meaning of numbers.

April 22: Recovered, almost: China’s early patients unable to shed coronavirus

• As of April 21, 93% of 82,788 people with the virus in China had recovered and been discharged, official figures show.
• Some patients are confined to test centers for at least 28 days and obtain two negative results before being allowed to leave.

Data analysis

Let us combine information from 2 articles listed above. If Covid19 test has false negative rate of 30% it means probability of passing 2 consecutive tests is:

0.3 * 0.3 = 0.09 or 9%

Since 93% of 82,788 infected people had been discharged we can estimate number of false negatives among them:

0.93 * 82788 * 0.09 = 6929

In plain words if Reuters numbers are true there have been close to 7 thousands people infected with Covid19 and showing no symptoms, released to the society. This should have caught editors’ attention if they still bother to employ one. Simple coin toss will produce 50% false negatives, so 30% is a huge number. In order to go below 1% false negatives, you need to run 4 consecutive tests if a single test false negative rate is 30%. Even 1% false negatives will result in around 700 infected patients release.

Now if Chinese authorities claim they have save general public from Covid19 by applying strict quarantine measures and isolating all cases, above numbers make the claim suspicious. Release of 7000 contagion sources to population without immunity would result in immediate surge of new cases. Let’s have a look at China cases reported since March:

We see daily cases trend toward 0 indicating no surge of new cases whatsoever. This can be explained in the following way:

1. General population build resilience to Covid19. This may not be the case at whole country level yet, but places which went over epidemic, like Wuhan, now have immune population. False negatives can be released with no substantial risk.
2. China understood from statistical data on Wuhan outbreak, Covid19 is initially deadly to a small fraction of population. Since vast majority of cases are either symptom free or mild population immunity builds quickly. Thus Covid19 is contagious, dangerous for individuals but innocuous for overall population.
3. Social distancing and quarantine help to manage outbreak, but are not essential to curb epidemic.

Assuming above is true why is China not willing to share the knowledge? Perhaps they see it as an opportunity to build economical advantage over other countries. EU and US economies under lock down are taking a heavy toll. They will likely slump into depression if Covid19 measures are not lifted fast. Why EU does not care to verify if Chinese scenario outlined above is true? We have plenty of data at our disposal to do it.