[R] Test For Difference of Betas By Group in car

[David Winsemius]

Sent from my iPhone

> On Jan 19, 2025, at 2:48 PM, David Winsemius <dwinsemius using comcast.net> wrote:
> 
> 
> Sent from my iPhone
> 
>> On Jan 19, 2025, at 1:57 PM, David Winsemius <dwinsemius using comcast.net> wrote:
>> 
>> I don’t understand why you don’t include the full text of the error.
>> 
>> —
>> David
>> Sent from my iPhone
>> 
>>>> On Jan 19, 2025, at 10:00 AM, Sparks, John via R-help <r-help using r-project.org> wrote:
>>> 
>>> Hello R-Helpers,
>>> 
>>> I was looking into how to test whether the beta coefficient from a regression would be the same for two different groups contained in the dataset for the regression.
>>> 
>>> When I put that question into google, AI returned a very nice looking answer (and a couple of variations on it).
>>> 
>>> library(car)
>>> data <- data.frame(income = c(30, 45, 50, 25, 60, 55),
>>>                 education = c(12, 16, 14, 10, 18, 16),
>>>                 gender = c("Male", "Female", "Male", "Female", "Male", "Female"))
>>> model <- lm(income ~ education * gender, data = data)
>>> # Test if the beta for "education" is significantly different between genders
>>> test <- linearHypothesis(model, "genderMale - genderFemale = 0")
> 
> That last line appears unlikely to be parsed correctly. In R a “=“ sign is interpreted as assignment whereas a “==“ (doubled equals) is a logical operator. Since I’ve only got a iPhone at hand I can’t test. In the future you should include full text of errors, preferably in the context in which they are returned.
> 
> As an experiment I asked ChatGPT your question an it suggested
> 
> library(car)
> data <- data.frame(
>  income = c(30, 45, 50, 25, 60, 55),
>  education = c(12, 16, 14, 10, 18, 16),
>  gender = c("Male", "Female", "Male", "Female", "Male", "Female")
> )
> model <- lm(income ~ education * gender, data = data)
> # Test if the effect of education differs by gender
> test <- linearHypothesis(model, "education:genderMale = 0")
> 
> But I have the same concern about that code as I had with whatever your AI produced.
> 
> —
> David

After looking at the second and subsequent example in `help(linearHypothesis, car)` I think chat GPTs attempt looks plausible.  The examples don’t use “==“ but they also use just the column names and not the coefficient labeling that you used. 

— 
David. 
> 
>>> print(test)
>>> 
>>> This, however, produces an error that I can't find a way to resolve.
>>> 
>>> Can this test actually be done in this manner, or is this a case of AI run amok.
>>> 
>>> Guidance would be appreciated.
>>> --John Sparks
>>> 
>>> 
>>> 
>>>  [[alternative HTML version deleted]]
>>> 
>>> ______________________________________________
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>>> PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>> 
>> ______________________________________________
>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>