Comparing each level of a factor to the global mean
Hi Jean, contr.treatment(4) shows what the default contrast matrix looks like for a factor with 4 levels. What function do I use to create a contrast matrix to compare each level with the global mean (four comparisons in total), and produce a table similar to `summary.lm`? Thanks, Shaun
On 26 June 2013 05:50, Adams, Jean <jvadams at usgs.gov> wrote:
Shaun,
See the help on contrasts ...
?contr.treatment
Jean
On Tue, Jun 25, 2013 at 7:07 PM, Shaun Jackman <sjackman at gmail.com> wrote:
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
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