Simulation: estimation and prediction at X = 5.5
Use this diagram to explain the difference between estimating the mean response at x and predicting a new response value at x. The estimate and prediction are identical but the targets are different — for prediction, there is a moving target — so the errors are different.
Click Accumulate then take several samples. The prediction error has greater spread than the estimation error.
Increase the sample size to 210. The error in estimating the mean becomes very small, but the prediction error is still quite large.