I have timeseries data with n=100 and have done a simple linear regression on the first 50 data points. What I'm interested in doing is seeing how good my y-hat line is at predicting the second 50 data points based on the xi values. I can certainly find the distance in y-value between the y-hat line and each of the second data points. However, I'm wondering where I go from there.
Thanks in advance.