The British Doctors' Study is an important study, which has followed participants for 60 years to Investigate the relationship between tobacco smoking and cause speci'd mortality among British doctors, In 1851, a questionnaire on smoking habits was sent to 49,913 male and 10,323 female doctor registered with the British General Medical Council, 34,440 male doctor and 6194 female doctors gave sufficient information to classify their smoking status (Doll and Peto, 1976; Doll of al,, 1960). The vital status of those doctors was followed up from the records of the Registrar General's Office, the British Medical Council, and the British Medical Association. The causes of death for 10,072 male and 1094 female doctors who had died during the first 20:and 22 years of follow-up respectively were ascertained from death certificates. The rate of death from lung cancer among smokers was compared with that among non-smokers. 1. What is the study type and design? 2. What is the best stansical measure