This is actually more like a Statistics problem:
I have a dataset with two dummy variables controlling three levels. The
problem is, one level does not have many observations compared with other
two levels (a couple of data points compared with 1000+ points on other
levels). When I run the regre
Do you have a reason to treat all 3 levels together and not have a separate
regression for each level?
--- On Tue, 1/7/08, rlearner309 <[EMAIL PROTECTED]> wrote:
> From: rlearner309 <[EMAIL PROTECTED]>
> Subject: [R] A regression problem using dummy variables
> To:
AIL PROTECTED]> wrote:
>
>> From: rlearner309 <[EMAIL PROTECTED]>
>> Subject: [R] A regression problem using dummy variables
>> To: r-help@r-project.org
>> Received: Tuesday, 1 July, 2008, 11:38 PM
>> This is actually more like a Statistics problem:
I think the covariance between dummy variables or between dummy variables and
intercept should always be zero. meaning: no sigularity problem??
rlearner309 wrote:
>
> This is actually more like a Statistics problem:
> I have a dataset with two dummy variables controlling three levels. The
>
On Wed, 2 Jul 2008, rlearner309 wrote:
I think the covariance between dummy variables or between dummy variables and
intercept should always be zero. meaning: no sigularity problem??
No. You can easily check that this is not true using the cov() function.
Indicator variables for mutually
I think it is zero, because you have lots of zeros there. It is not like
continous variables.
Thomas Lumley wrote:
>
> On Wed, 2 Jul 2008, rlearner309 wrote:
>
>>
>> I think the covariance between dummy variables or between dummy variables
>> and
>> intercept should always be zero. meaning:
rlearner309 wrote:
I think it is zero, because you have lots of zeros there. It is not like
continous variables.
Think again. The sum of products may be zero, but that is not the
covariance. And don't dismiss Thomas, he is usually right.
Anyways, the coefs of dummy variables represent dif
"which group contrasts you want to look at" can you clarify me on that
statement?
--- On Thu, 3/7/08, Peter Dalgaard <[EMAIL PROTECTED]> wrote:
From: Peter Dalgaard <[EMAIL PROTECTED]>
Subject: Re: [R] A regression problem using dummy variables
To: "rlearner309"
09; Peter Dalgaard
Cc: r-help@r-project.org
Subject: Re: [R] A regression problem using dummy variables
"which group contrasts you want to look at" can you clarify me on that
statement?
--- On Thu, 3/7/08, Peter Dalgaard <[EMAIL PROTECTED]> wrote:
__
sorry, made a stupid mistake.
I got it.
thanks a lot!
Peter Dalgaard wrote:
>
> rlearner309 wrote:
>> I think it is zero, because you have lots of zeros there. It is not like
>> continous variables.
>>
>>
> Think again. The sum of products may be zero, but that is not the
> covariance. And
"V&R's MASS book" can you give the full name of that book
--- On Thu, 3/7/08, Bert Gunter <[EMAIL PROTECTED]> wrote:
From: Bert Gunter <[EMAIL PROTECTED]>
Subject: RE: [R] A regression problem using dummy variables
To: [EMAIL PROTECTED]
Cc: r-help@r-project.org
Dat
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