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

[Shaun Jackman]

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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>
>