# How to test whether individual fits to regression line or not

I have a defined regression model for the healthy control (HC) group, with corresponding CIs of coefficients and of E(Y).

I would like to test whether individuals belonging to another population (patients), one by one individually, are fitting or not the healthy control regression line. I have both Xs and Y values for the new individuals.

I'm not sure about how to proceed: should I test the individual coefficients compared to the ones of the HC regression line, or should I predict the new Y values based on the HC model and test whether these Y values are significantly different from the actual ones?

• How many predictors does the HC model have? – James Phillips May 20 at 20:37
• @JamesPhillips 4, corresponding to a cognitive ability measure (the same) across 4 timepoints close in time (we're looking for cognitive performance fluctuations, and whether these are different between healthy controls and patients, at the individual level). – Agnese Giacomello May 22 at 14:22

linearHypothesis(lm_healthycontrols,  c("(Intercept) = 5.5", "x1 = -1", "x2 = -2", "x3 = -2"))