[R] variance component analysis for nested model

[Russell Senior]

Given a set of data:

> names(data)
[1] "city"     "house"     "visit"    "value"

I am looking for a way to compute the variance components of the
nested model (ie, visit 1 at house 2 at city 3 isn't related to visit
1 and house 2 at city 4), but different houses in the same city may be
related, and different visits to the same house are probably related.
I want to be able to compute how much of the total variance of "value"
is explained by each of these.  How can I do that in R?

Thanks!

-- 
Russell Senior         ``shtal latta wos ba padre u prett tu nashtonfi
seniorr at aracnet.com      mrlosh''  -- Bashgali Kafir for ``If you have
                         had diarrhoea many days you will surely die.''