Tobacco and Public Health - TCSC Indonesia

it seems likely that some of this variation may have arisen from including in the control
series patients hospitalized for diseases that later proved to be smoking-attributable.
In any case, epidemiologists agreed that sound evidence was essential, given the high
prevalence of smoking and the social and economic implications of the results.
The need for cohort studies
Doll and Hill realized that the simplest way to attempt to replicate the findings of the
case-control studies, using a different methodology, was to obtain information on the
individual smoking habits of a large number of people, and to follow them to determine
whether an individual’s smoking habits predicted the risk of developing disease
(Doll 1998b). Such cohort studies would need to be large so that they could provide a
sufficient number of events to be informative within a reasonable time period. They
would need to collect questionnaire information on smoking behavior, since such
information was not then (and is not now) routinely collected on vital statistics
records. In turn, the cohort studies would provide several important advantages over
case-control studies. They could examine the relationship between smoking and many
different end points, not just a single disease. This was important, because more than
70 per cent of deaths caused by smoking result from diseases other than lung cancer
(CDC 2002). The comparison group in cohort studies could be defined as lifelong
non-smokers, thus avoiding the problem of including patients with other smokingattributable
diseases in the control group. Finally, cohort studies are intuitively more
understandable than case-control studies, because they reflect the desired temporal
sequence in which exposure precedes disease.
The earliest cohort studies
MICHAEL J. THUN AND JANE HENLEY 21
The two earliest cohort studies of tobacco use and mortality were the British Doctors
Study, which began in the United Kingdom in 1951 (Doll and Hill 1954, 1956), and the
Hammond Horn or Nine-State study, initiated by the American Cancer Society (ACS)
in 1952 (Hammond 1953, 1954). Both of these were designed to facilitate enrollment
and follow-up of large populations. For instance, the physicians who participated in
the British Doctors Study were identified from the Medical Register of the United
Kingdom and followed through the Registrars General, the British Medical Association,
and the General Medical Council (Doll and Hill 1956). The information on clinical
diagnoses and cause of death was thought to be more accurate for doctors than for the
general population. Similarly, the extensive network of local volunteers for ACS provided
an extraordinary human resource to enroll, and help to follow, large prospective
epidemiological studies in the United States (Thun et al. 2000). Both the ACS cohorts
and the British Doctors Study provided effective conduits for disseminating information
about the adverse effects of tobacco use. Publicity about the studies caused many
doctors in the United Kingdom and United States to stop smoking, well ahead of the
general public.