Impact of - IDL-BNC @ IDRC - International Development Research ...

especially in the absence of complementary evidence from animal or human
studies.
The assumptions and limitations of epidemiology are no less complex: human
experimentation is not acceptable and the mobility and participation of individuals
cannot be neatly controlled; exposures must have taken place and may
be diluted, intermittent, combined, or multiple; some potential outcomes may
take many years (perhaps generations) to develop and may not even be
foreseeable, e.g., diethylstilbestrol and transitional cell carcinoma of the
vagina in first-generation offspring of exposed women (Bornstein et at. 1988);
and loss of information can occur at any level (identification of population,
adequacy of records, tracing persons, nonresponse, survivor bias, and
sample-size limitations).
The findings of both disciplines are frequently at variance. For example,
caffeine can produce chromosomal aberrations in cell culture, but there is no
evidence of a relation to human or animal cancers, stillbirths, or birth defects
(Thilly and Call 1986). Such a finding maybe of no pathologic importance, but
should at least stimulate further study by both disciplines. The use of saccharine
was banned in many countries based on rat studies indicating a link to
bladder cancer (Gaylor et at. 1988). This was met by initial scepticism in some
quarters due to a lack of supporting data.
The role of epidemiology
Epidemiology is viewed by many as the core science of public-health practice
and is of equal relevance to the more specialized fields of occupational and
environmental health. In assessing human exposures, including pesticide use
in developing countries, epidemiologic techniques can be used to address six
aims:
To characterize distributions of risk factors, disorders, or disease;
To reveal associations between factors and disease;
To assess evidence of causality;
To develop strategies for prevention, intervention, and control;
To evaluate impact of potentially harmful exposures and corrective
measures; and
To contribute to regulation.
The application of epidemiological-study designs to risk assessment, prevention,
and control of potentially harmful occupational and environmental
exposures is conceptually straightforward, but can be very difficult in practice
because of problems of technique as well as logistics. Furthermore, the results
of such studies in themselves constitute only one input into a complex
19