标题: 2022.02.25 一些国家的covid-19死亡人数是否造假？ [打印本页] 作者: shiyi18 时间: 2022-2-26 05:36 标题: 2022.02.25 一些国家的covid-19死亡人数是否造假？ More equal than others
Are some countries faking their covid-19 death counts?
An elementary statistical test casts doubt on some abnormally neat numbers
FEB 25TH 2022
Sometimes the numbers are simply too tidy to be believed. Irregular statistical variation has proven a powerful forensic tool for detecting possible fraud in academic research, accounting statements and election tallies. Now similar techniques are helping to find a new subgenre of faked numbers: covid-19 death tolls.
That is the conclusion of a new study to be published in Significance, a statistics magazine, by the researcher Dmitry Kobak. Mr Kobak has a penchant for such studies—he previously demonstrated fraud in Russian elections based on anomalous tallies from polling stations. His latest study examines how reported death tolls vary over time. He finds that this variance is suspiciously low in a clutch of countries—almost exclusively those without a functioning democracy or a free press.
Mr Kobak uses a test based on the “Poisson distribution”. This is named after a French statistician who first noticed that when modelling certain kinds of counts, such as the number of people who enter a railway station in an hour, the distribution takes on a specific shape with one mathematically pleasing property: the mean of the distribution is equal to its variance.
This idea can be useful in modelling the number of covid deaths, but requires one extension. Unlike a typical Poisson process, the number of people who die of covid can be correlated from one day to the next—superspreader events, for example, lead to spikes in deaths. As a result, the distribution of deaths should be what statisticians call “overdispersed”—the variance should be greater than the mean. Jonas Schöley, a demographer not involved with Mr Kobak’s research, says he has never in his career encountered death tallies that would fail this test.
That should make it easy to pass. And the vast majority of countries reporting data to the World Health Organisation do. This does not mean that their death tallies were necessarily accurate—undercounting still plagues many countries with insufficient testing (which is why The Economist estimates the pandemic’s death toll using excess deaths). But it does suggest that the numbers reported are not being deliberately tampered with.
Yet data from 17 countries had the opposite pattern. In many weeks, the variance of each distribution was less than the mean. This is a statistical smoking gun. “It seems reasonable to conclude that there’s no way these are independent observations,” says David Steinsaltz, a professor of statistics at the University of Oxford.
Imputing motives is harder. A benign explanation would be bureaucratic bottlenecks in processing death certificates. Yet there are other irregularities: the usual drop-off in weekend reporting is often absent. According to Mr Kobak, the likelier explanation is cackhanded tampering.
The Russian numbers offer an example of abnormal neatness. In August 2021 daily death tallies went no lower than 746 and no higher than 799. Russia’s invariant numbers continued into the first week of September, ranging from 792 to 799. A back-of-the-envelope calculation shows that such a low-variation week would occur by chance once every 2,747 years. ■
Sources: “Underdispersion in the reported covid-19 case and deathnumbers may suggest data manipulations”, by D. Kobak, working paper, 2022; Our World in Data; JHU CSSE
