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Re: dummy coding of categorical variables results in zero coefficients a
From: |
EKreyken |
Subject: |
Re: dummy coding of categorical variables results in zero coefficients and standard errors |
Date: |
Wed, 20 Dec 2023 10:44:18 -0800 |
Hi Time,
Answering the stats stuff only:
Without seeing the data, I can’t make a definitive call on this, but it seems
that calculations for the t test cannot be completed properly. This indicates
either a) no shared linear variability in your XY variables (incredibly rare to
get perfect 0), forcing the t test to do a division of 0 over the variability
in X, or b) your X variable has no variability (also incredibly rare), forcing
the t test to divide shared linear variability over 0.
You may have one of several problems.
1) dummy coding wasn’t done accurately and you don’t have enough variability in
your X variable
2) you have a perfect non-relationship in those variables (very very rare)
3) you have a non-linear relationship that is really acting weird with the
t-test, but it wouldn’t yield a n/a.
Check the following:
A) get the averages and standard deviations for all predictors. They should
have a standard deviation above 0 for the test to work.
B) plot the data for those specific predictors (X) against the response (Y)
variable. You should end up with 2 separate graphs. Check for linear /non
linear patterns.
C) plot the residuals (google/youtube knows how to do this). Check for
“randomness” vs patterns: patterns in the residuals are bad.
If you’re interested, I offer stats consulting.
Cheers,
Elisabeth
On Dec 20, 2023, at 1:47 AM, tim.goodspeed@btinternet.com wrote:
found?