Hi Rick, First I want thank you for many great posts in your blog on IML which I, as well as many others, benefit a lot from. We use that formula for the confidence interval of predictions in our model, and we are asked to provide a reference where the formula comes from, or a deriviation if no such reference exists. We actually use regression with auto-regressive errors in many of our models, so we do want to be assured of the correctness of the formula. thanks, Jonathan ... View more