I am having a problem and I know a way to solve but don't know how to statistically implement it. I'm trying to summarize the problem in a simple way here:

Say I am regressing a dataset, X agianst another dataset, Y.

Now, if I wish to capture how much is the disagrement of this regression line from a hypothetical "perfect regression line" that passes exactly through all observed data points (may be with keeping the intercept same as before).

Then, I wish to ADD that disagreement-component (of X and Y) to another dataset, say M.

Now, how do I capture the disagreement, and then add that to another dataset !

Any help would be very much appreciated.

kind regards,

Chintanu