OK, I feel stupid asking this, but I am positive you all will know exactly what I should do here.
I have a simple regression situations (small sample sizes; n=13-18), and a few observations that are different with respect to a suite of characteristics that can be generalized by a single dummy variable (ex. south site vs. north site). If I had a roughly even number of sites in each category (north or south) with a decent spread over the X value, I would consider ANCOVA (I guess), but I do not. I have ~3 (of 13-18) sites that belong to "south" that if removed would lead to a nice linear relationship among the "north" sites. What would be the most appropriate method for dealing with these data. It seems like there has to be a better way than running the models with and without these sites and then doing some hand waving.
Please let me know if you have any good ideas.