Re: Why Helmert contrasts?

Anon. wrote:
> Can someone out there explain why anyone would want to use Helmert 
> contrasts?
>
> Bob

From the SPSS help files...

Helmert. Compares the mean of each level of the factor 
(except the last) to the mean of subsequent levels.

This yields k-1 orthogonal contrasts.  One might use this in 
a drug study with a placebo (group 0) and several increasing 
doses.  If there were 3 doses (groups 1-3), the contrasts 
would be:

[0] v [1 2 3]
[1] v [2 3]
[2] v [3]

Cheers,
Bruce
--
Bruce Weaver
[EMAIL PROTECTED]
www.angelfire.com/wv/bwhomedir/