Understanding one in 100,000

What does this tiny probability look like?

The EMA stated there was a plausible link between the Oxford-AstraZeneca (Vaxzevria) vaccine and rare blood clots. The European Medicines Agency said the probability of this kind of blood clot was “very low”. With millions vaccinated, very rare side effects can emerge.

The Paul-Ehrlich-Institut reported brain blood clots with low platelets in one in 100,000 vaccinations. The MHRA figure was a little lower: at about 0.4 in 100,000. The disparity comes from coverage, case definition, study period, and population differences.

What does one in 100,000 look like?

One in 100,000 is a very small probability. It is challenging to think about this chance.

We can put 100 dots in a row. We can then stack 100 rows of those dots on top of each other. The square of 100 is ten thousand. The probability of one in 10,000 then looks like:

You should be able to see the orange marker. (Image: R Pubs)

Ten stacks of those squares is then 100,000 dots:

Spotting the orange dot may be more difficult this time. (Image: R Pubs)

What else has these odds?