[R] aov documentation page: question

[AJ Smit]

Dear all
I was looking at the aov documentation page and came across the 
following which seems like a contradiction to me:

 This provides a wrapper to |lm| for fitting linear models to balanced 
or unbalanced experimental designs. (I presume 'This' refers to aov)

and
|aov| is designed for balanced designs, and the results can be hard to 
interpret without balance

So, do I use it for unbalanced designs?
Thanks,
AJ
--
Dr Albertus J. Smit
(Marine Ecologist/Algal Biologist)
School of Biology and Conservation Science
Faculty of Science
University of KwaZulu-Natal
Westville Campus
P/B X54001
Durban
4000
South Africa
Tel. (031) 260 7472
Fax (031) 260 7364

Please find our disclaimer at http://www.ukzn.ac.za/disclaimer

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[R] SE for combined data

[AJ Smit]

Dear all

I have just had the question from a colleague. I know that it is not directly related to R (I will probably use R to do the analysis), but I hope someone can give us some insight:

Thanks,
AJ Smit


I sampled populations of a seaweed in the intertidal in order to estimate
the standing biomass of that seaweed at that site.
Due to clumped distribution patterns, I chose a stratified sampling system,
as follows. In each of three subjectively defined biomass classes (low,
medium and high biomass density), four quadrats (usually) were haphazardly
placed, and the biomass in those quadrats harvested. This provided an
estimate of the biomass density present in that biomass density class. The
area of ground covered by that biomass density class was also estimated,
and, by combining the estimated biomass density and the area covered by that
biomass density class, the total biomass in that biomass density class was
estimated. When the estimated biomass in the three biomass density classes
was combined, I had a figure for the standing biomass for that site..
So, for each biomass density class, I have a number of biomass density
estimates (usually, but not always, four), and an estimate of the area
covered by that class.
I repeated this at a number of sites. Biomass density classes were not
necessarily the same between sites.
Given that I can calculate measures of variation for each biomass density
class, is there a way to combine these data, presumably weighted by the area
covered by each biomass density class, and calculate the standard error for
the final biomass estimate at each site?

Thanks
Neil
--
~~~
Dr Albertus J. Smit
Department of Botany
University of Cape Town
Private Bag Rondebosch
7700
Cape Town
SOUTH AFRICA

Tel. +27 21 689 3032
Fax  +27 21 650 4041
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