Godolphin, PJ;    Godolphin, EJ;      (2019)    Robustness of crossover trials against subject drop-out - Examples of perpetually connected designs.                   Statistical Methods in Medical Research , 28  (3)   pp. 788-800.    10.1177/0962280217736541 <https://doi.org/10.1177/0962280217736541>.       Green open access