A two-sample censored-data rank test for acceleration
by Breslow, Edler, Berger
http://ascopubs.org/doi/10.1200/JCO.2014.55.2208
http://dx.doi.org/10.1080/19466315.2016.1257436
https://www.onlinelibrary.wiley.com/doi/abs/10.1002/sim.5440