Evidence-Based Practice for Nurses

Case Reports or Series

Case reports or series are used to describe rare diseases or
outcomes. The purpose of these studies is generally to describe
new diseases, explain a change in disease patterns, or alert
the healthcare community to unusual signs and symptoms in
an individual patient (case report) or rare findings among a
few patients (case series). Here is an example of a case series:

In the period October 1980–May 1981, 5 young men, all active homosexuals,

were treated for biopsy-confirmed Pneumocystis carinii pneumonia at 3 different

hospitals in Los Angeles, California. Two of the patients died. All 5 patients had

laboratory-confirmed previous or current cytomegalo-virus (CMV) infection

and candidal mucosal infection. . . . The diagnosis of Pneumocystis pneumonia

was confirmed for all 5 patients antemortem by closed or open lung biopsy.

The patients did not know each other and had no known common contacts or

knowledge of sexual partners who had had similar illnesses. Two of the 5 reported

having frequent homosexual contacts with various partners. All 5 reported us-

ing inhalant drugs, and 1 reported parenteral drug abuse. Three patients had

profoundly depressed in vitro proliferative responses to mitogens and antigens.

Lymphocyte studies were not performed on the other 2 patients. (AIDS.gov, n.d.)

This edition of the Morbidity and Mortality Weekly Report was the first official
report of what later became known as the AIDS epidemic (AIDS.gov, n.d.).

The advantage of case reports is that this design can be used to describe un-
usual signs and symptoms so that healthcare providers may be able to identify
commonalities among patients when a new disease appears in a population.
Case reports also can be helpful in identifying when a current disease mutates.
The disadvantage of case reports is the lack of a comparison group. Without a
comparison group, there is no mechanism to test hypotheses.

Ecologic Studies

Correlational studies are used when the unit of analysis is a population, not an
individual, and are known as ecologic studies. These studies are used to compare
a summary measure of disease frequency across summary measures of exposure.
Merriam-Webster defines exposure as “the condition of being subject to some
effect or influence.” As a result, the nurse is evaluating group-level rates of disease
and exposures. When data from individuals are reported as group information,
they are said to be aggregate data. For example, suppose a nursing administrator
has to report salaries for staff nurses. Rather than telling each individual’s salary,
the nurse administrator would aggregate the data and report the average salary by
unit or by shift. Reporting aggregate data in this manner preserves confidentiality.

Ecologic studies can be used to compare distribution and determinants of
diseases across many different population units such as states, counties, zip

KEY TERMS

case reports

or series:

Epidemiologic

reports used to

describe rare

diseases or

outcomes

ecologic studies:

Correlational

studies that

are population-

based rather than

individual-based

exposure: Contact

with a disease or

disease-producing

agent

aggregate data:

Data collected

from individuals

that are grouped

to represent a

population

FYI

Researchers use descriptive study designs

to generate hypotheses to examine different

types of phenomena. These types of studies

include case reports or series, ecologic stud-

ies, and cross-sectional studies.

8.5 Descriptive Study Designs 205