A couple of weeks ago, a news story flashed by me on twitter: 49% of the UK have slower-than-average broadband. It was followed more or less immediately by a swathe of snipey comments saying ‘isn’t that the definition of an average?’

To which the smart-arse answer is, no, there is no average defined as the 49th percentile. That would be daft. Once you’ve sighed and said ‘well, 50% then!’, I’d grimace a little and say ‘It’s the definition of an average - the median - but that’s probably not what you meant.’

In fact, the report here doesn’t specify which average they used to define their benchmark of 6.742 Mb/s. They also have their units mixed up and call it Mbp/s, which is just plain wrong. But I digress. In likelihood, the average they mean is the mean - all the speeds added up and divided by the number of trials.

I’m not sure that’s actually the real mean, though. I think to find a mean broadband speed, you need to add up the total amount of data transferred in the tests and divide by the total number of seconds the tests took - just like with normal speed. For instance, if you drive 10km at 60km/h (not kmp/h, as I’m sure uswitch would have it) and then 10km at 30km/h, you’d have travelled 20km in 30 minutes - an average speed of 40km/h (not the 45 you might have expected).

So, the moral of the story:

• when you say average, say which average you mean
• if you want to sound like an idiot, use the wrong units
• when you’re finding a mean speed, be very careful to do it properly.

Anything I missed?