Hello, We've got a dataset with several variables, one of which we're using to split the data into 3 smaller subsets. (as the variable takes 1 of 3 possible values).
There are several more variables too, many of which we're using to fit regression models using lm. So I have 3 models fitted (one for each subset of course), each having slope estimates for the predictor variables. What we want to find out, though, is whether or not the overall slopes for the 3 regression lines are significantly different from each other. Is there a way, in R, to calculate the overall slope of each line, and test whether there's homogeneity of regression slopes? (Am I using that phrase in the right context -- comparing the slopes of more than one regression line rather than the slopes of the predictors within the same fit.) I hope that makes sense. We really wanted to see if the predicted values at the ends of the 3 regression lines are significantly different... But I'm not sure how to do the Johnson-Neyman procedure in R, so I think testing for slope differences will suffice! Thanks to any who may be able to help! Doug Adams ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.