R中的Quade测试

Question

我想在R中使用多个协变量执行Quade测试。我知道命令quade.test并且我已经看到了以下示例：

## 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)

我的问题如下：我怎么能引入一个以上的协变量？在此示例中，协变量是Store变量。