ElizaD - 10 August 2007 10:20 AM

*On average between 50 and 60 volcanoes erupt every year* and *Between 50 and 60 volcanoes erupt every year* mean precisely the same thing, so “on average” is redundant. I don’t buy the fact that the writer means that sometimes that average could be 41 or 78 in any one year. I just think he’s being sloppy. If you’re talking about averages, why not give a precise figure, eg On average 57.1 volcanoes erupt every year?

How does .1 of a volcano erupt? Just a teeny little pardon-me burp of an eruption or what?

Edit: Why does Dr Techie have to go on holiday when we need him?

Quick second edit: Not that I associate Dr Techie with burping, let alone excessive intake of alcohol, of course. Perish the thought.

All of which goes to show that even well educated people do not understand averages.

The average of 0 and 109 is 54.5. To say the average of those two numbers is between 50 and 60 is perfectly true, if you told someone to expect about 55 eruptions and there were over 100 they wouldn’t think much of your estimation skills.

I don’t buy ‘t buy the fact that the writer means that sometimes that average could be 41 or 78 in any one year.

No, he doesn’t try to say any thing like that. The NUMBER of eruptions in a year could be 41 or 78 - there is no average in a year, there is a count in a year.

Some examples:

In these 10 years the number of eruptions are:

41, 55, 55, 55, 55, 55, 55, 55, 55, 55, 78

The average number of eruptions per year is 55.9

The number of eruptions in an average year is 55.

Now a different set of 10 years:

41, 41, 41, 41, 41, 41, 78, 78, 78, 78

The average number of eruptions per year is 55.8

The number of eruptions in an average year is 41.