A geometric approach to tree shape statistics

This article presents a new way to understand the descriptive ability of tree shape statistics. Where before tree shape statistics were chosen by their ability to distinguish between macroevolutionary models, the ``resolution'' presented in this paper quantifies the ability of a statistic to differentiate between similar and different trees. We term this a ``geometric'' approach to differentiate it from the model-based approach previously explored. A distinct advantage of this perspective is that it allows evaluation of multiple tree shape statistics describing different aspects of tree shape. After developing the methodology, it is applied here to make specific recommendations for a suite of three statistics which will hopefully prove useful in applications. The article ends with an application of the tree shape statistics to clarify the impact of omission of taxa on tree shape.