Mean what you say, and say what you mean

Written by Web News Editor on . Posted in News

According to an item on the BBC website “Astronomers currently estimate that every star in the night sky hosts, on average, 1.6 planets” Is that poor statistics or poor use of English?
If every star “hosts, on average, 1.6 planets”, then our near neighbour Proxima Centauri, for example, hosts on average 1.6 planets – and so, for that matter, does the Sun.
What could that possibly mean? Perhaps the number of planets around Proxima Centauri varies over time with an average of 1.6? Of course not!
In fact, the intended meaning is that the average number of planets per star is 1.6. It is a poor use of English to say that every star has, on average, 1.6 planets. Poor use of language in presenting statistical information often leads to poor understanding.
Compare the three statements “every woman has, on average, 1.9 children”, “the average woman has 1.9 children”, and “women have, on average, 1.9 children”. The first, mirroring the star quotation above, is pretty much nonsense; the second seems to imply that there is such a person as the average woman and that she has a fractional number of children; the third puts the matter clearly and intelligibly. It’s not difficult to use or understand the third form of words, but the first two are unfortunately common in journalism.

Neil Sheldon has taught at The Manchester Grammar School for 40 years. He is a Chartered Statistician and Fellow of the Royal Statistical Society. He has been an RSS Guy Lecturer since 2007.  He is also course leader for the Certificate in Teaching Statistics offered by the RSS Centre for Statistical Education

Mean (arithmetic mean)

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