One of my specialties is period analysis, identifying and quantifying periodic and pseudo-periodic fluctuations in time series. The essence of periodic fluctuations is that they repeat. It’s not just that the signal forever goes up and down, possibly in random fashion; there’s a pattern to the ups and downs, and that pattern repeats in cycles — not necessarily perfectly (in the case of pseudoperiodicity), not even necessarily forever, but repeats often enough and regularly enough that we can, at least in the short term, have some idea of what the next cycle will look like, given that we know the most recent cycles.
This may end up being one of my more controversial posts, because I’m going to expound on one of my “pet peeves” in science: the claim of periodic or pseudoperiodic behavior when none exists. It might just be the most common mistake made by working scientists, and it makes its way into the peer-reviewed literature all the time. It just goes to show that peer review is a necessary, but hardly a sufficient, condition for correct results.
