I have two groups (A & B).

First step In each group, I am trying to find the relationships between dependent variable (flow) and 2 covariates (total rain and preflow).

Should I:

  1. Do a multiple regression with the two covariate, or
  2. Divide the dependent variable (flow) by one of the covariate (preflow) to create a sort of index, then regress that index against another covariate (total rain)?

Second step I now need to compare between group A and B. Whichever method that i have used in Step 1 above, how should i proceed?

Should I:

  1. Just find the difference between coefficients of regression for individual regression A and B, or
  2. Do a multiple-regression between group A and B, or
  3. (each of value A) - (each of value B) and then regress against covariate?

I hosted the data file here.

Thank you


Just run a multiple regression with Group as a categorical variable along with the covariates you mentioned. The coefficient on the categorical variable (Group B) will be the difference between default (Group A) and Group B.

Now, if you are also interested in how your groups A and B interact with other covariates (if you think the impact of other covariates is different for each group and it matters), you may include interraction terms as well.


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