On 14 Dec 1999 16:38:00 -0800, [EMAIL PROTECTED] (Rich Strauss)
wrote:
< snip >
> I'll just add the usual caveat that hasn't yet been mentioned in these
> responses about proportions: the transformations, use of the binomial, and
> comment about proportions just being means all assume that the data really
> are proportions, not ratios -- that is, that the denominator is fixed among
> all values, not variable. The problem is that many people use the terms
> interchangably, talking about proportions or percentages when they're
> actually dealing with ratios.
Ratios are one problem. Right -- be careful about them.
But Proportions are another problem when the denominators are not the
same. If one subject is scored a proportion which is none-for-one,
0/1= 0%, that is usually a score with far less "information," and
bigger standard error on the response, than if another subject rates
0/20=0%.
I am not referring just to zero -- if subjects have data based on
vastly different Ns, it may be wasteful to lump them based on
percents. One approach that seemed useful for some analyses of
genotypes was: do separate analyses for different N, and then combine
those analyses.
--
Rich Ulrich, [EMAIL PROTECTED]
http://www.pitt.edu/~wpilib/index.html
