Monday, March 26, 2007

How do you spell "heteroskedasticity"?

Econometrics is full of long and difficult words: stochastic, kurtosis, multicollinearity, autocorrelation and - perhaps worst of all - heteroskedastcity.

You may like to know that the correct spelling of heteroskedasticity was actually the subject of a one page article in the journal Econometrica. In the March 1985 issue J Huston McCulluch argued that there should be a k in the middle of the word and not a c. His argument was that the word had been constructed in English directly from Greek roots rather than coming into the English language indirectly via the French.

The earliest use that McCulloch could find for either heteroskedastcity or heteroscedastcity was in a 1923 statistics text by Truman L Kelley. However John Aldrich in contributing to a website on the earliest known uses of some words in mathematics states that 'The terms heteroscedasticity and homoscedasticity were introduced in 1905 by Karl Pearson in "On the general theory of skew correlation and non-linear regression," Drapers' Company Res. Mem. (Biometric Ser.) II. Pearson wrote, "If ... all arrays are equally scattered about their means, I shall speak of the system as a homoscedastic system, otherwise it is a heteroscedastic system." The words derive from the Greek skedastos (capable of being scattered).'

One might ask the question as to why is it that econometricians, statisticians and other scientists use Greek words such as this as labels for these concepts when ordinary English words might do just as well. In part the answer might be to avoid confusion with the ordinary English usage of a word. For example the word "investment" when used by an economist carries a very specific meaning that might not be apparent even to a well-educated non-economist. Perhaps at least having a special word for the concept makes a reader check exactly what it means rather than making an assumption that it must mean what he thinks it does.

Of course what can happen is that these special words can then make it into ordinary language. In case you think that would be impossible for the word "heteroskedasticty" I invite you to read the paragraph about the distribution of rabbits around the UK in the Smallweed column of the Guardian for 23rd July 2005. "Have these brainboxes never heard of the concept of heteroscedasticity?" Yes, we have but you spell it with a k and not a c!

[1] J Huston McCulloch. On Heteros*edastcity. Econometrica 1985, Vol 53 No 2 (March) p483.
[2] John Aldrich. Earliest Known Uses of Some of the Words of Mathematics (H). Accessed March 2007.
[3] David McKie. Armageddon isn't upon us. The Guardian 31st August 2006.
[4] Smallweed column 23rd July 2005


Blogger Joe said...

Another good reason for words like "heteroskedastic" in the modern age - they are extremely google-able. Try searching for an econometrics term like "significant" or "powerful" on google - it is next to impossible.

6:10 AM  

Post a Comment

<< Home