[R] Quade test

[Fernando Sánchez Lasheras]

Hello to all the list members. I would like to perform a Quade test with
more than one covariate. I know the command quade.test and I have seen the
example below:

## Conover (1999, p. 375f):
## Numbers of five brands of a new hand lotion sold in seven stores
## during one week.
y <- matrix(c( 5,  4,  7, 10, 12,
           1,  3,  1,  0,  2,
          16, 12, 22, 22, 35,
           5,  4,  3,  5,  4,
          10,  9,  7, 13, 10,
          19, 18, 28, 37, 58,
          10,  7,  6,  8,  7),
        nrow = 7, byrow = TRUE,
        dimnames =
        list(Store = as.character(1:7),
             Brand = LETTERS[1:5]))
y
quade.test(y)

My question is as follows: how could I introduce more than one covariate? In
this example the covariate is the Store variable. But what if I also have
another covariate i.e.: the the number of inhabitants of the town in which
each store is located.

Thanks in advanced for your help!

Fernando