[R] Compare linear regressios for significant differences of the slopes

[Rainer M Krug]

Dieter Menne wrote:
> Rainer M Krug wrote:
>>> I have (8 measures * 96 groups) = 768 datasets for which I did linear
>>> regressions using lm().

Sorry for my (probably incorrect) usage of "group" and "measure".

Here a (probably better) description of my design:

I ran 96 different simulations (spread of a species along a transect) 
over four generations, based on different parameter sets. These resulted 
in 96 results (groups). Now I have 8 different ways to describe the 
result of one simulation based on x individuals further away then 
distance d, where x is replaced by 1, 5, 10, 50, 100, 500, 1000 and 5000 
(measures). For each group / simulation, I did linear regressions for 
each measure

 > lm.measure_1 <- lm(distance ~ generation)
...

resulting in lm.measure_1 to lm.measure_8

Within each group (based on one simulation), I get a different slope for 
each measure.

What I want to know is if these resulting slopes differ within one group 
/ simulation.

>>>
>>> Now I want to compare the slopes for each of the 8 measures in each of 
>>> the 96 groups. As I understand , I can not use
>>>> anova(lm1, ..., lm8)
>>> as the lm1 ... lm8 are based on different datasets.
>>>
> 
> Instead of doing this in two steps, you would better use lme in package nlme to
> test the hypothesis in one run. I don't understand the details of you design,
> but is looks like the oxboys example in Pinheiro/Bates (the book of nlme) could
> give you a first starter.
> 
> Dieter
> 
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-- 
Rainer M. Krug, Dipl. Phys. (Germany), MSc Conservation
Biology (UCT)

Department of Conservation Ecology and Entomology
University of Stellenbosch
Matieland 7602
South Africa

Tel:		+27 - (0)72 808 2975 (w)
Fax:		+27 - (0)21 808 3304
Cell:		+27 - (0)83 9479 042

email:	RKrug at sun.ac.za
       	Rainer at krugs.de