Exoplaneteers Keep Calling Plots "Allan Variance" Plots When They Aren't

Abstract

I highlight that there is a substantial number of papers (at least 11 published since 2024) which all refer to a specific type of plot as an "Allan variance" plot, when in fact they seem to be plotting the standard deviation of the residuals versus bin size. The Allan variance quantifies the stability of a time series by calculating the average squared difference between successive time-averaged segments over a specified interval; it is not equivalent to the standard deviation. This misattribution seems particularly prolific in the exoplanet transit spectroscopy community. However, I emphasize that it does not impact the scientific analyses presented in those works. I discuss where this confusion seems to stem from and encourage the community to ensure statistical measures are named correctly to avoid confusion.