[R] summary.lm for post-hoc tests

[Dimitri Liakhovitski]

Check this out:

http://www.rforge.net/doc/packages/NCStats/compSlopes.html

However, it looks like one need to install NCStats
(http://www.rforge.net/NCStats/files/).
Or is there a more "mainstream" method of running multiples
comparisons among slopes?

Dimitri


On Sat, Oct 30, 2010 at 1:20 PM, Alex Bokov <bokov at uthscsa.edu> wrote:
> Let's say I've run Anova(lm(y~a*b)) and found the a:b interaction to be
> significant. Now I'm interested in which specific level combinations of a
> and b significantly differ from the control group. Can I use the t-tests
> from summary(lm(y~a*b)) to answer that question?
>
> I saw no mention of multiple comparison in the documentation for summary.lm,
> so am I right in assuming I need to run p.adjust on the p-values column?
>
> Thanks.
>
> PS: I am aware of TukeyHSD and that works fine if a and b are both factors.
> However, if 'a' is numeric and I'm interested in which levels of 'b' have a
> different slope from the control group, TukeyHSD cannot do that, and I'm
> hoping the above can.
>
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-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com