[R] Crawley's book on S-Plus and one strangeness

[Matej Cepl]

Douglas Bates wrote:
> Can you be more specific?  Which datasets?
> 
> > And one small question aside: I was very much surprised (in this
> > book as well as on this list) how many times people use
> > sqrt(var(x)) when what they want to say (IMHO) is sd(x). Is it
> > just a macho way to show that I understand more complicated
> > things, or is there any real difference between the two?

There is a big number of them (the book has 761 pages and no CD,
so all data used are I suppose from S-Plus), but let's make
a couple of examples:

	* blowfly -- ``The Australian ecologist A.J.Nicholson reared
	  blofly larvae on pieces of liver in laboratory culture for
	  almost 7 years'' ... used for analysis of cyclicity and acf
	  function,
	* rats -- data from Sokal and Rohlf (1995) describing an
	  experiment with three treatments to six rats; used for ANOVA
	* regression -- weight of caterpillars relates to the tannin
	  content of their diet
	* etc. I really do not think, that six pages long list makes
	  any difference.

> The var function was available in S long before the sd function was
> introduced and many 'old-timers' instinctively use sqrt(var(x)) rather
> than sd(x).  The sd function ends up calling sqrt(var(x, na.rm =
> na.rm)) when argument x is a vector.

I see.

Matej

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