etc.
Uses of descriptive studies
They can be done fairly quickly and easily.
Allow planners and administrators to allocate resources
Provide the first important clues about possible determinants of a disease (useful
for the formulation of hypotheses)
Types of descriptive studies
a) Case reports and case series
Case report:
a careful, detailed report by one or more clinicians of the profile of a single
patient.
The individual case report can be expanded to a case series, which describes characteristics
of a number of patients with a given disease.
Uses
Important link between clinical medicine and epidemiology
One of the first steps in outbreak investigation
Often useful for hypothesis generating and examining new diseases, but conclusions
about etiology cannot be made.
b) Ecological studies:
data from entire populations are used to compare disease
frequencies between different groups during the same period of time
or in the same population at different points in time.
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Example:
Countries with low cigarette consumption have lower lung cancer rates than
those countries with high cigarette consumption.
Ecological studies are usually quick and easy to do and can be done with already
available information.
Since ecological studies refer to whole populations rather than to individuals, it is not
possible to link an exposure to occurrence of disease in the same person.
c) Cross-sectional studies
A cross-sectional (prevalence) study provides information concerning the situation at a given
time. In this type of study, the status of an individual with respect to the presence or absence
of both exposure and disease is assessed at the same point in time.
Usually involve collection of new data.
In general, measure prevalence rather than incidence
Not good for studying rare diseases or diseases with short duration; also not ideal for
studying rare exposures.
For factors that remain unaltered over time, such as sex, blood group, etc., the cross-
sectional survey can provide evidence of a valid statistical association.
As can be noted from the above explanation, a cross-sectional study can be either analytical
or descriptive, according to its purpose. If data are collected both on exposures and
outcomes of interest, and if the data are analysed so as to demonstrate differences either
between exposed and non-exposed groups, with respect to the outcome, or between those
with the outcome and those without the outcome, with respect to the exposure, then this is an
analytical cross-sectional study. If the information collected is purely of a descriptive nature,
not involving the comparison of groups formed on the basis of exposure or outcome status,
then this is a descriptive cross-sectional study. Often a cross-sectional study may have both
descriptive and analytical components.
Nowadays, there is an increasing emphasis on the value of longitudinal studies in which
observations are repeated in the same community over a prolonged period (i.e., longitudinal
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studies provide the required data at more than one point in time unlike cross- sectional
surveys) .
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