topic Multivariate regression by category or subgroup in Statistical Procedures

Multivariate regression by category or subgroup

laurenhosking — Wed, 18 Nov 2020 11:19:07 GMT

I’m using a Multivariate regression to model the Total volume as a function Of two variables Units and Price.

However I’m not sure wether to model the total volume as a whole or whether to model it by subgroups of brand. How would I go about finding this out?

I have performed cluster analysis for the category as a whole and by brand but unsure how to interpret the results in order to answer this question

Re: Multivariate regression by category or subgroup

Rick_SAS — Wed, 18 Nov 2020 11:50:09 GMT

I think you are asking about a classical ANOVA model that asks whether the mean Volume differs according to the brand. All you need to do is use the CLASS statement to specify the brand variable, then include that variable in your model. FOr example, if you are using PROC GLM, the code looks like this:

proc glm data=Have plots=all;
class Brand;
model Volume = Units Price Brand;
quit;

Re: Multivariate regression by category or subgroup

laurenhosking — Wed, 18 Nov 2020 11:55:47 GMT

Fabulous thank you, and if they do differ then I would need to model my regression by subgroups which is brand?

Re: Multivariate regression by category or subgroup

Rick_SAS — Wed, 18 Nov 2020 12:05:20 GMT

Correct. You can look at the F-tests and p-values for the Type 3 sums of squares to assess whether an effect is statistically significant.

Re: Multivariate regression by category or subgroup

laurenhosking — Wed, 18 Nov 2020 15:33:46 GMT

I have observed that 2 of my groups behave the same but 1 behaves differently. So I decided to use brand as a subgroup.

However doing this I’ve been told my R-square value should be close to 1 but it’s not it’s as low as 0.3 in certain cases. Does this matter?

Re: Multivariate regression by category or subgroup

PaigeMiller — Wed, 18 Nov 2020 15:58:28 GMT

In an ideal world, R-squared should be close to 1. But different data has different amounts of noise, and so a r-squared of 0.3 may be the proper value for this data. The real question in my mind would be to look at the root mean square error reported by SAS and decide if this is an acceptable level of variation (or not). If, for example, you have some idea of measurement variability or sample-to-sample variability, and the root mean square error is somewhat close, then I'd say that's fine. Or, if the confidence intervals around your predictions or around you parameter estimates are usable, then that's fine as well. All of this is context and problem dependent, there are no rules of thumb, every data set is different, every application is different, every use is different.