I have a regression model with $R^2$ value. I am trying to use this model on a different data set to see how well the model predicts this data.
So far I have used the model with the 'new' data to make predictions and then I have used a fitted line plot to asses how well the new predictions compare with the real data.
I would like a way of including the original $R^2$ value in this new analysis.
E.g one model has r sq 95.5%, when I plot the predicted values (using this model) against the real data the r sq is 74%.
Is there a better way I can do this analysis rather than just reporting the new $R^2$ value?