characteristics of that patient. Only subsequent con-
trolled research can pin down the exact causes of, or
factors influencing, change.
Epidemiological Methods
Epidemiologyis the study of the incidence, preva-
lence, and distribution of illness or disease in a
given population. Several terms are commonly
used in epidemiology. Incidence refers to the rate
of new cases of illness that develop within a given
period of time, whereas prevalence refers to the
overall rate of cases (old or new) within a given
period.Incidence gives us some sense of whether
the rate of new cases of the illness or disorder is
on the increase (e.g., is the rate of newly diagnosed
AIDS cases increasing this year compared to last
year?).Prevalencerates estimate what percentage of
the target population is affected by the illness or
disorder. For example, the lifetime prevalence rate
of schizophrenia is estimated at 1%, suggesting that
a member of the general population has 1 chance in
100 of developing this disorder in his or her
lifetime.
Historically, epidemiology has been most
closely associated with medical research designed
to help understand and control the major epidemic
diseases, such as cholera and yellow fever. The sim-
ple counting of cases is central to this research
method. The expectation is that analyzing the dis-
tribution of cases in a community or region and
uncovering the distinguishing characteristics of the
affected individuals or groups will teach us some-
thing about the causes of a particular disease and the
methods by which it spreads. Epidemiological
methods can also be quite important in identifying
groups of individuals who are at risk.
A well-known example of epidemiological
research is the studySmoking and Health(Surgeon
General, 1964). This study linked cigarette smoking
with lung cancer by the simple methods of count-
ing and correlating. Although there was great
debate as to whether smokingcausedlung cancer,
there were definite relationships and associations
between smoking and lung cancer (e.g., about
90% of lung cancer in males was associated with
cigarette smoking, and the amount and duration
of smoking were positively correlated with the
probability of cancer). It is true that epidemiological
research frequently suggests the possibility of multi-
ple causation (several factors must be present before
the disease occurs, or the greater the number of
associated factors that are present, the greater the
risk of the disease). It is equally true that obtained
correlations suggestcauses rather than definitively
prove causation. However, the entire story of cau-
sation need not be known before preventive steps
can be taken. Thus, we may not be sure that smok-
ing causes lung cancer, or we may believe that some
inherited predisposition interacts with smoking to
produce cancer. Nevertheless, we know that groups
of males who quit smoking reduce their risk of lung
cancer.
As another example, in the field of mental
illness, a number of studies have pointed out the
relationship between schizophrenia and either
socioeconomic class or factors of social disorganiza-
tion (Faris & Dunham, 1939; Hollingshead &
Redlich, 1958). Again, though such results hardly
convey the essence of schizophrenia, they do tell us
about major demographic factors that are associated
with its prevalence. Armed with this information,
clinicians can identify people whose potential vul-
nerability to schizophrenia is high. They can then
establish special programs that will provide early
diagnostic evidence of its onset in such people, or
they can establish treatment programs that will be
readily available to those at risk of developing
schizophrenia.
Much epidemiological research is based on sur-
veys or interviews. However, survey and interview
data present a number of issues and potential prob-
lems. For example, how do we define a mental
health problem, and having done so, where do
we locate cases for counting? Checking only clinics
and hospitals means ignoring other possible locales.
These difficulties are magnified when we become
interested in milder forms of dysfunction. In effect,
we need objective methods of defining and mea-
suring a problem. Further, we need survey proce-
dures that will enable us to estimate the problem’s
true incidence or prevalence and not just to locate100 CHAPTER 4