The announcement, by the media, of a million daily cases in the world, has prompted some commentators to affirm that with more than 200,000 contaminations per day, France represented 20% of new cases on the planet. It’s wrong.
You asked us about two statistics that have made the headlines in recent days. The first is the record number of contaminations recorded in France on a given day: 208,000 Wednesday (a total approached the next day with 206,000 new cases). The second being the announcement, widely relayed by the media, of a million daily cases in the world, a record there too.
“If we cross these 2 pieces of information, we could conclude that France has contributed over the past 24 hours to 20% of global contaminations… that seems huge, doesn’t it ???”, write to us.
We can bet that Florian Philippot made the same quick calculation, evidenced by his tweet:
This calculation is however incorrect. The two statistics (that of France, and that calculated at the global level) are not comparable.
The figure of 208,000 contaminations in France therefore corresponds to the number of positive results recorded on Wednesday. Daily statistics by result date should always be taken with caution: in fact, they are subject to high volatility, since they vary depending on the day of the week (for example they will be much lower on weekends or on Monday). For this reason, it is always best to calculate the daily seven-day average, which smooths out these daily variations or other statistical accidents.
The figure of 1 million new daily cases in the world which has been widely reported by the media is precisely a daily average calculated over seven days (between 23 and 29 December). As indicated in its dispatch AFP at the origin of this figure: “On average, 1,045,000 new daily cases were detected over the period, up 46% from the previous week, according to an AFP count on Thursday established from reports communicated by each country.” This means that over this week, there were just over 7 million new cases recorded on the planet (7.3 million precisely). But with strong variation depending on the day. Thus, on December 25, “only” 500,000 new cases were recorded worldwide. As of Wednesday, that figure was 1.73 million. A strong difference which can be explained as much by a lower figure due to Christmas Day, but also by the growing epidemic dynamic in several regions of the world.
It does not make sense to compare data taken on a specific day (for France) with data calculated over seven days (for the world).
If we want to make a comparison, we must apply to France the method of calculation used by AFP for its world figure. This gives this: over the period from 23 to 29 December, France experienced just over 730,000 new cases, or a daily average of around 104,000 new cases. The fact that this value is significantly below the Wednesday value (208,000 cases) is logical, for two main reasons: the seven-day average incorporates the “weak” figures of 25 (holiday) 26 (a Sunday) and 27 (since few tests were done on weekends, it makes sense that few results were recorded on Monday). It also incorporates values at the start of the period which were lower, the omicron contaminations not yet having “exploded” (on December 23, a little over 91,000 new cases were recorded).
By calculating an average over seven days, there were therefore, for the period from 23 to 29 December, a little more than 1 million daily cases in the world, and a little more than 100,000 cases in France, like the shows this graphic from the Our world in Data site. A ratio of 1 to 10.
1.73 million new cases recorded worldwide on Wednesday
And if we decided, conversely, to relate the 208,000 contaminations recorded in France on Wednesday to comparable data at the global level, we would have to take the number of new cases recorded worldwide for the single day of Wednesday (and no longer average over seven days). That is 1.73 million new cases, again according to Our world in data. A record since the start of the pandemic. Like France, several other countries affected by the omicron outbreak that day broke the record for new cases recorded, as summarized by journalist Vincent Glad.
On Wednesday, France (208,000 new cases) therefore represented around 12% of new contaminations recorded worldwide (1.73 million). As shown in this second graph (still from Our world in Data).
Whatever indicator we decide to use (figures for the day of December 29, or figures for the weeks of December 23 to 29), France does not represent 20% of new cases.
Finally, remember that the most rigorous way to count new cases is to do it by collection date – and not by result date – and on average over seven rolling days. But these data are only available with a delay of several days.
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