The general practice observation subset included periods of observation, deaths, and other relevant
information obtained while women were under observation by general practitioners, up to their point of
being lost to general practice follow-up, death, or December 1996 when general practice follow-up
ended (whichever came first). This subset contained information about use of hormone replacement therapy while under general practice follow-up, as well as comprehensive data about the type and duration of oral contraceptives used.