I have two time series which are sampled at the exact same times. I would like to calculate a confidence interval either for the ratio between the two or the difference between the two. The values tend to be somewhat similar, but both have a large amount of what looks like random noise superimposed on them (much larger than the potential difference, at any particular point in time). What is the appropriate method to calculate a confidence interval in this case?
P.S. The data is very different from being normal; it is roughly flat-top, pretty similar shape (but perhaps shifted) for the two series.