Making predictions
In many cases the purpose of model fitting is to make predictions about the response given a value of the predictor.
It is important to remember that making predictions outside the observed range of the data (known as extrapolation) is risky. It is impossible to be sure that the fitted relationship extends beyond the observed range.
For a Budget of 100 million $ the average retained impressions per week is 64.9 million. The 95% confidence interval (CI) 50.2 to 79.5 million is the uncertainty in the mean estimate. The 95% prediction interval (PI) 18.2 to 111.6 is the interval we would expect a single future observations to lie within.
