In this short paper with Roberto Salguero-Gómez and Connor Bernard we show that a commonly used discrete-time formula for Keyfitz entropy does not preserve the simple relationship with increasing, decreasing, and constant mortality that the continuous-time formula had. We propose a new discrete-time formula instead, and show that the proposed new metric correctly classifies increasing, decreasing, and constant mortality survivorship curves. We also show that the previously used metric is particularly bad at classifying species with low life expectancies leading to a spurious correlation between the shape and the pace of life when this metric is used.

Our response to Pen&Flatt (2021) is now accepted by Proceedings of the Royal Society B: Biological Sciences: https://royalsocietypublishing.org/doi/10.1098/rspb.2022.1101