Epidemiological Equivocacy as a Source of Uncertainty in Risk Assessment. T. Sly, School of Environmental Health, Ryerson Polytechnic University, Toronto, Canada
Epidemiological inquiries frequently result in less enlightenment
than expected. While details of new risks to health appear to
be published almost daily, the impact is muddied by weak effects,
inconclusive associations, and apparent ambiguity in the research.
Contradictions between studies, in particular, are the
source of media debate and even popular satire. Society's perception
is one of questioned credibility, regardless of how rigorous or
flawless the investigation, and society often fails to detect
what it is looking for in published science: a clear, definitive,
conclusion that will inform decision making.
At the same time, the recognition and interpretation of uncertainty
is highly desirable in today's science, and if the uncertainties
were routinely explicit, and public debate about them encouraged,
much of the anxiety about risks to health might actually diminish.
Investigators are thus obliged to tread cautiously between the
dangers of declaring (unfounded) confidence on the one hand, and
inadvertently generating concern from the method of inquiry on
the other. This paper identifies five sources of uncertainty
and ambiguity in health and medical research.
1. Equivocacy due to the framework for investigation
Awareness of the importance of environmental and social factors in the disease process had been the norm prior to the mid-nineteenth century, but the emerging concept of ill health as a purely biological phenomenon, and the rise of "scientific" - particularly allopathic - medicine, narrowed the focus. During the second half of the twentieth century, however, social, economic, behavioural, and environmental determinants returned to a more central position, but at a cost. While investigations of specific agents in most cases follow a straightforward sequence of steps, with results that exonerate or condemn that agent, explorations into the roles of interdependent factors are complex in design, difficult in analysis, and frequently enigmatic in outcome. As the base for inquiry has broadened, the conclusions have become increasingly equivocal.
2. Equivocacy inherent in the nature of the current topics and of their risks to health
Early investigations in epidemiology sought to identify and contain disease entities largely of an acute and infectious nature. Although infectious diseases still demand the attention of public health workers, the focus of much of today's epidemiology is upon cardiovascular diseases and cancers, and prospective studies into these conditions may need to gather 10-20 years' worth of data. As our understanding of synergism and interaction between biologic, genetic, and psychosocial factors increases, the results of research will inevitably appear more complex.
3. Equivocacy from the conservative methods, models, and tools of modern research
The credibility of the "scientific method" stems from
the conservative statistical analyses by which hypotheses are
tested. Instead of assembling supportive evidence to validate
hypotheses, they are tested in a "null" form: - that
there is no effect, no difference, no association, etc. Only
when the null hypothesis is rejected at a satisfactory level of
significance, can the original hypothesis be entertained. Such
a process will allow us to state, for instance, ".. that
the exposure and the outcome appear to be associated - but with
a probability that this association might still have arisen by
chance alone in up to 5% of repeated trials". A result
in this form, while accurate, remains inherently inconclusive
for legal and other non-scientific arguments.
Although the usefulness of the result can be improved by measuring
dose-response Gradients between exposure and outcome, or the strength
of the association, the inferences drawn from hypothesis-testing
can easily misinform the lay person.
4. Equivocacy from emphasis, de-emphasis, omission, or addition
Subtle adjustment of reported results from proprietary research
or research sponsored or commissioned by interested parties has
been the subject of extensive examination. It is not beyond the
realm of possibility that for political, or perhaps commercial
reasons, the commissioners of any study may choose to stress "inconclusive"
findings.
The lay press frequently misconstrues results to be more conclusive
than they really are: the "breakthrough" phenomenon.
But blame must also be attributed to researchers and their institutions
who for diverse reasons often issue news releases far too early,
and with not enough attention to how the message might be received.
5. Equivocacy from poor design and implementation
Insufficient attention to the design, sampling, data Gathering,
analysis, and interpretation, can manifest as a weak, ambiguous,
or even completely spurious finding when the result should have
been quite definite - or as strong association when in reality
there was none. In either instance, the misleading results can
be expected to increase the apparent inconsistency between studies.
Both circumstances are unacceptable. Several criteria with potential
for weakening the validity and accuracy of studies in the chronic,
non-infectious realm include:
Final considerations
Even with optimal data and analysis, a conclusion "beyond
all reasonable doubt" may not be attained, nor in some instances
should one be expected. To postpone decisions affecting the health
of people or the environment until such time as incontrovertible
evidence becomes available and accepted may be irresponsible and
unethical. In such instances, the "burden of proof' should
be weighed against the "burden of prudence."
At all stages of the reporting and publication of research,
however, the full extent of the uncertainties and limitations
must be stated and interpreted Science cannot provide unequivocal
assurance of safety, yet society may become more reassured were
it to hear that admission more clearly.