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### What Does a Twofold Increase Mean?

```Date: 01/23/2004 at 04:57:51
From: Laura
Subject: 2-fold increase

What does a onefold increase mean?  Is a twofold increase simply twice
the amount?  What about a threefold increase?  I'm not used to this
terminology of using "fold."  Does it refer to powers or multiples?

```

```
Date: 01/23/2004 at 09:40:45
From: Doctor Peterson
Subject: Re: 2-fold increase

Hi, Laura.

The suffix "-fold" refers to multiples.  "Onefold" means a whole,
"twofold" means twice, "threefold" means three times as much.

According to Merriam-Webster (m-w.com), "twofold" means

1 : having two parts or aspects
2 : being twice as great or as many

and the suffix "-fold" means

1 : multiplied by (a specified number) : times -- in adjectives
<a sixfold increase> and adverbs <repay you tenfold>
2 : having (so many) parts <threefold aspect of the problem>

Although some people might quibble over "twofold increase," arguing
that it has to mean the _increase_ itself is twice the original
value, and thus a tripling, a quick web search makes it clear that
the phrase universally refers to a mere doubling: an increase _to_
twice the original amount.  See this page for a discussion of the
quibble with reference to a similar, but more controversial, phrase:

Percent Greater Than vs. Increased
http://mathforum.org/library/drmath/view/61774.html

I have never heard of a "onefold increase," and don't find the phrase
on the web.

If you have any further questions, feel free to write back.

- Doctor Peterson, The Math Forum
http://mathforum.org/dr.math/
```
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