I am (prospectively) evaluating a NHS health board wide quality improvement initiative aiming to reduce exposure to high-risk prescribing. I am expecting a time lag in the intervention effect, but it is hard to predict how large the lag will be. It is also possible that an initial impact will diminish after a while, resulting in a post-intervention shape of the data that may be difficult to model. I am therefore considering comparison of the AUCs of the extrapolated baseline trend (which I expect to be roughly linear) and the post-intervention outcome. I am looking for comments on this idea and any previous experience (ideally published) with this approach.