?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.aulast=Royston&rft.au=Royston%2C+P&rft.aufirst=P&rft.atitle=Power+and+sample-size+analysis+for+the+Royston%E2%80%93Parmar+combined+test+in+clinical+trials+with+a+time-to-event+outcome&rft.volume=18&rft.date=2018&rft.issue=1&rft.title=Stata+Journal&rft.pages=3-21&rft.issn=1536-867X&rft.genre=article