[R] Comparing each level of a factor to the global mean

[Shaun Jackman]

Hi,

I've used `lm` to create a linear model of a continuous variable
against a factor variable with four levels using an example R data set
(see below). By default, it uses a treatment contrast matrix that
compares each level of the factor variable with the first reference
level (three comparisons in total). I'd like to compare each level
with the global mean (four comparisons in total), and produce a table
similar to `summary.lm`. How do I go about this?

```r
model <- lm(weight ~ Diet, ChickWeight)
summary(model)
```

Thanks,
Shaun