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When central banks raise or lower interest rates the radio announcer will say for example:

an increase of one half of one percent

Informally people use half a percent instead, which is less wordy, but is it also incorrect? Ngrams analysis shows publishers favour the longer version, although the short form seems to be gaining some traction.

Thinking about it, I'd never offer someone one half of one pizza; that sounds weird. However, I believe of is necessary here, in combination with an article, quantifier or pronoun. Is this correct?

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it does seem to be accepted and understood, but it never really made any sense to me either, because percent is a ratio of two things and is not a unit per se. –  horatio Apr 19 '11 at 19:38
    
@horatio: Physicist sometime treat "percent" exactly as a unit, albeit a dimensionless one. This does not bother us; indeed "radians" is another pure number that is used as a unit. –  dmckee Apr 19 '11 at 21:40
    
Most announcers I know say "50 basis points" or "50 points" to mean 0.5%. –  Mikel Apr 19 '11 at 23:07
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@horatio, you are right in that when someone says "half a percent" in this way they almost invariably mean "half a percentage point": that is to say, that interest rates have risen from 1.0 to 1.5% rather than 1.0 to 1.005%; the former is of course a rise of 50%. –  Brian Hooper Apr 20 '11 at 5:56
    
@horatio: percent can be used to define a ratio, but it is not defined as such. The Bureau International des Poids et Mesures simply defines % as a representation of the number 0.01. See this document, at page 50 (or 140 if you can't understand French, but bare in mind the French version is more extensive): bipm.org/utils/common/pdf/si_brochure_8.pdf –  nico Apr 20 '11 at 13:31
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3 Answers

up vote 11 down vote accepted

In short: yes, “half a percent” is accepted usage, even in formal writing.

To back it up: the New Oxford American English lists percent as both an adverb (“a 1.8 percent increase”) and a noun (“a reduction of half a percent or so in price”). Note that the second example nicely answers your question.

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The phrase half a(n) X is a well-established English idiom. The use of percent here is a straightforward application of the idiom:

  • half a cup of water
  • half a loaf of bread
  • half a dozen
  • half a percent

In financial contexts, the more formal version may be preferred, but there's nothing wrong with the informal equivalent.

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Also note that the article can precede "half" in this kind of construction: "Today the Dow Jones Industrial Average fell a half percent." Or, "He brought home a half dozen roses." –  The Raven Apr 19 '11 at 19:30
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Yes.

People in the financial world will sometimes say 50 basis points (itself often shortened to 50 bips in speech). A basis point is one percent of one percent.

But in colloquial, mainstream English, half a percent is perfectly fine.

PW

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