Notes on f4-ratio estimation

The f4-ratio estimation is a popular technique for estimating gene flow proportion as a ratio between two f4-statistics. We point out the underappreciated fact that the root is not important in f4-ratio estimation, making the technique highly versatile. We study robustness and the bidirectional case. We introduce an enhanced branch statistic fB for detecting tentative gene flow events in a large phylogenetic tree, which has favourable properties compared to Malinskys branch statistic fb.