# How to express reduction from 10 or 100 billion to 1 billion

What word or phrase would correctly describe the reduction of 10 billion to 1 billion, and from 100 billion to 1 billion?

I need to have it sound scientific: Reduce an amount from 1010 to 109, and from 1010 to 108.

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Decimate could describe a reduction of a population by 1/10th. en.wikipedia.org/wiki/Decimation_%28Roman_army%29. But Josh's "Order of Magnitude" sounds more scientific. From 100 billion to 1 billion would be "two orders of magnitude smaller." – rajah9 May 9 '13 at 13:56

I believe the correct expression is to reduce by an order of magnitude / reduce by 2 orders of magnitude.

http://en.wikipedia.org/wiki/Order_of_magnitude

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There are quite a few other ways of expressing the same thing - here are some examples:

Shrink by [100*(1 - final / initial)] %

Shrink to [100 * final / initial] % of the initial value

Shrink by a factor of initial / final

Experience a change of [100*(final / initial - 1)] %

Make sure you specify appropriate units for whatever is changing in size / quantity / whatever, or your statement will lose meaning when taken out of context.

If you are dealing with changes of multiple different orders of magnitude, then that form of expression may be more appropriate - it's equivalent to counting the 9s in the % reduction, which gets tedious if you have a lot of them. For an audience not familiar with orders of magnitude, some of the alternatives might be easier to explain.

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You could say "reduce to a tenth / hundredth of its original value"

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Another wedding? I think not. You've been absent from ELU for some time now. Hope everything is OK. – Mari-Lou A Nov 3 '13 at 8:37
Relieved to see that you made an appearance on 11 Nov, but I do miss reading your contributions and the inevitable reference to Chambers. – Mari-Lou A Nov 15 '13 at 23:10