so “on average” is redundant

Hurrah for ElizaD.

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.

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

Patronising remarks are always unwelcome and often uninformed.  As you are now proving. 

I understand averages perfectly.  I happen to think that the wording of the sentence leads to confusion, as everyone is now arguing about exactly what he does mean.  His expression, not my understanding, is at fault.  This is an example of poor English.

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.

No, they do not mean precisely the same thing.  The first statement, as has been pointed out by several people, means that there may well be some years when there are more than 60 volcanoes erupting and some when there are fewer than 50.  The second eliminates both those possibilities.  The first statement also implies that the deviation from the range of 50 to 60 will probably not be very great or very frequent.

“On average between 50 and 60 volcanoes erupt every year”

Happydog answers the question for me.

It depends on what your purpose is. If you’re doing math, then an average is a specific number, but “average” isn’t always used in a perfectly mathematical sense. “The average Joe” isn’t a mathematical idea, it’s more of a feeling. If you want to convey a feeling instead of mathematical precision, then you use a statement such as the one in the documentary. Even documentaries have to be entertaining and feelings always connect better than concepts.

Dave Wilton:

Average, in the general sense, simply means the expected value that one one should obtain. Average, in the general sense, simply means the expected value that one one should obtain. It is often used more specifically to be synonymous with the arithmetic mean, but this is not the only or “correct” sense. So the narrator of the documentary is using the word quite properly.

“On average” is a turn of phrase, and does not refer to a precise figure.  I am not sure whether or not this sentence intends to convey a running average*.  Any sentence which leads to uncertainty or misunderstanding is poorly constructed.  I am fully aware that the sentence could be taken literally, but I do not think that this is what the author intended. 

*Please - no more lessons in maths.

I would also note that—aside from the question of how the average is obtained—the number may have a certain imprecision even for a given year. E.g., it may be reasonable to say “between 50 and 60 volcanoes erupted in 2006”, since there are surely uncertainties about what constitutes a volcano or exactly when an eruption occurred. Does a smoke plume in Antarctica shown by satellite photography qualify as a volcano? If there are events on two sides of a given mountain are there two volcanoes? Does some very small eruption qualify? Are undersea events included? Etc.

I am not sure whether or not this sentence intends to convey a running average

If I were that average, I’d have been running (for my life) about fifteen postings back. What a bashing the wretched thing’s had! Nobody but a vulcanologist or an insurance actuary is likely to want to know with any precision how many volcanoes erupt in a given time period, or to worry much about what constitutes an eruption....so I suppose a vague statement was not out of order. But I still wish that fellow had left “average” out. The word has too many associations for someone who was involved in industrial quality control for many years.

If venomousbede would care to reveal (roughly ;-) where “between 50 and 60 eruptions occur on average each year”, i’ll make sure to exclude the place from my vacation plans. Volcanic eruptions are wonderful..... when viewed from100 km away.

(Edited to remove superfluous word)

I waited a few days for the discussion of the language to be thrashed a bit before injecting this little tidbit.

If you prefer you could substitute ambiguity in the reporting time period for ambiguity in the average. usgs volcanowatch reports:

During the past 20-30 years, there have been an average of 60 volcanic eruptions per year based on the records kept by the Smithsonian Institution’s Global Volcanism Program (GVP). The number of volcanoes erupting in any given year has varied between about 50 and 75.