[R] (g)lm ordinal or scaled values?

[Liaw, Andy]

Ordinal variables should be stored as ordered factors in R.  See ?ordered.

Andy 

From: Knut Krueger
> 
> There is a difference in the p- value from   0.000 and 0.012 
> when I am 
> using SPSS.
> 0.000 when I am using the independent variable as scaled 
> 0.012 if I am using the variable as  ordinal.
> 
> The independent variable is ordinal but it seems that R is 
> using the variable as an scaled, because the P- Value is 
> computed with 4.66e-06
> 
> 
> so I am not sure which description I am misunderstanding:
> SPSS;:
> Covariates. Scale predictors 
> <javascript:popup(N2C5F1_term,N2C5F1_def);> 
> should be selected as covariates 
> <javascript:popup(N2B079_term,N2B079_def);> in the model. Within 
> combinations of factor levels (or cells 
> <javascript:popup(N2AE3F_term,N2AE3F_def);>), values of 
> covariates are 
> assumed to be linearly correlated with values of the 
> dependent variables.
> (A variable can be treated as scale when its values represent ordered 
> categories with a meaningful metric, so that distance comparisons 
> between values are appropriate. Examples of scale variables 
> include age 
> in years and income in thousands of dollars.)
> 
> Factors. Categorical <javascript:popup(N2AD73_term,N2AD73_def);> 
> predictors should be selected as factors 
> <javascript:popup(N2B481_term,N2B481_def);> in the model. Each level 
> <javascript:popup(N2B937_term,N2B937_def);> of a factor can have a 
> different linear effect on the value of the dependent variable.(A 
> variable with a discrete number of values; an ordinal or nominal 
> variable. Categorical variables are often used as grouping 
> variables or 
> factors.)
> 
> The data : http://biostatistic.de/temp/testr.csv
> 
> lm.data<-lm( dependent ~ var2,family = gaussian)
> 
> I don't know whether anybody could explain me the difference between 
> SPSS and R results but if there are different results then 
> one of them 
> is wrong :-(
> And I do not know which of them.
> I hope I explained the problem understandable
> 
> Regards Knut
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
> 
>