Friday, February 10, 2012

The mangling of statistics

I don't commute as much as I used to so there is more time to study the web. This morning a story about Sainsbury's changing their advice about when to freeze food, on the BBC news site, caught my eye.

"The average UK family wastes up to £50 worth of perfectly good food a month."

Sorry, but the author of this sentence. and it is not clear who is the author, is writing nonsense. Either "the average family wastes £xx" where average denotes either the arithmetic mean of families sampled or the median (but whatever it is, you should tell us anyway) Or "some families waste up to £50". But you cannot have "up to" being the maximum in the same phrase as "average". If you still don't get this point, and would like to, consider this sentence:
"The average Premier league footballer scores up to 38 goals a season". Obviously some footballers, a small number one imagines, might score a lot of goals. The average footballer must score a lot less given that teams play roughly 50 competitive games a season and 1 or 2 goals a match is a reasonable amount to get. So this sentence is simply wrong.

The horrible wording that gets me angry is "up to". Everybody uses it in adverts when they are trying to lie. Broadband suppliers talk about speeds "up to " 24mbs or whatever, utterly meaningless because if you are considering switching the only speed that matters is the one you will get. Comparison  and insurance ads talk about savings "up to" some figure that they never explain. And now the BBC has joined in.

When I am King, anyone using "up to" without fully qualifying what they mean, in text at least as large as the headline, will go to the Tower, will go directly to the Tower without passing Go and will stay there until they pay a fine up to £25,0000.

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