To be clear, this:
>> How can I get the output to show all 3 groups that I have inputted? There
>> are only group 2 and group 3 on the output, group 1 is missing. Also there
>> is a subgroup (subgroup 1) of the total 9 subgroups missing. I would like
>> to see the p-value of the missing group and missing sub-group even though
>> I'm sure they are not significantly different (>0.05).
shows a fundamental lack of understanding of the basic ideas of linear
modeling (since it's basically nonsense -- an impossibility). You
would do well to contact a local statistician to help you out.
Cheers,
Bert
On Thu, Oct 14, 2010 at 12:50 PM, Joshua Wiley wrote:
> Hi Robert,
>
> In R, the default treatment contrasts for factor class variables in
> regression treats the first level as the reference group when creating
> the contrast matrix for the regression, so it is not really a matter
> of changing the formula.
>
> This might provide some insight:
> http://www.ats.ucla.edu/stat/r/library/contrast_coding.htm
>
> There are many ways to handle categorical data, and without knowing
> exactly what you want, it is difficult to give any sound suggestions.
> It really depends on your question.
>
>
> Cheers,
>
> Josh
>
>
> On Thu, Oct 14, 2010 at 12:34 PM, Robert Quinn wrote:
>> I have the following formula for a linear model:
>>
>> z <- lm(y~x + factor(a) + factor(b), data=NT2010)
>>
>> where a (groups) and b (Sub-groups) are categorical variables (factors), x
>> is a continuous covariate, and y the response variable. Since b is nested
>> within a, the formula can also be written as:
>>
>> z <- lm(y~x + factor(a) + factor(a)/factor(b), data=NT2010)
>>
>> and the same output is achieved when summary(z) is called.
>>
>> How can I get the output to show all 3 groups that I have inputted? There
>> are only group 2 and group 3 on the output, group 1 is missing. Also there
>> is a subgroup (subgroup 1) of the total 9 subgroups missing. I would like
>> to see the p-value of the missing group and missing sub-group even though
>> I'm sure they are not significantly different (>0.05). How do I change the
>> original formula to get all groups and sub-groups outputted?
>
>>
>>
>> [[alternative HTML version deleted]]
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>
>
> --
> Joshua Wiley
> Ph.D. Student, Health Psychology
> __
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Bert Gunter
Genentech Nonclinical Biostatistics
467-7374
http://devo.gene.com/groups/devo/depts/ncb/home.shtml
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