Evaluating the strength of the evidence obtained with quantitative designs includes
evaluating the timing of data collection. The time dimension of a study may
be classified as retrospective, cross-sectional, and longitudinal or prospective.Retrospective Designs
Retrospective designs may also be referred to as ex post facto, which means
after the fact. When designing retrospective studies, researchers start with the
DV and look back in time to determine possible causative factors. Retrospective
designs are considered to be after the fact because the DV has already occurred,
which means that the IV cannot be manipulated and subjects cannot be ran-
domly assigned. Thus, retrospective designs are never experimental in nature.
Retrospective designs are often used in epidemiological studies. For example,
causes of AIDS were discovered by researchers who started noticing an unusual
increase in the number of cases of Kaposi’s sarcoma occurring in young men
(Gallo & Montagnier, 2003). By taking careful histories, researchers were able
to look back in time to determine behaviors and risk factors common to men
who developed AIDS. Behaviors were compared with behaviors of men who
did not have the disease. This type of retrospective study is called a case-control
study because researchers started with a group of people who already had the
disease. Identifying smoking as a cause of lung cancer also resulted from exam-
ining retrospective data. In both of these examples, retrospective designs were
appropriate because it would have been unethical for researchers to deliberately
expose subjects to either the HIV virus or tobacco smoke.
When conducting quality control studies, researchers often use retrospective
designs. In these types of studies, researchers may want to gather information
about an organization’s status related to a patient problem such as falls. Chart
audits can be done to determine the number of falls that occurred in the past
6 months. Information can be gathered on patients who have fallen to identify
potential causative factors such as age, diagnoses, units where falls occurred, and
staffing levels at the time of falls. Thus, retrospective studies can provide important
data using nonexperimental designs. However, because retrospective designs
are not experimental, a disadvantage is that researchers cannot say definitively
that the IV caused the DV. Instead, researchers can conclude that there is an
increased likelihood or probability that the IV caused the outcome in the DV.Cross-Sectional Designs
Cross-sectional studies are nonexperimental designs that researchers use to
gather data from a group of subjects at only one point in time. Cross-sectional
designs provide a snapshot by collecting data about the IV and DV at the same
time. Because data are collected at one time, it is difficult to establish causeKEY TERMS
retrospective
designs: Research
designs when
researchers look
back in time to
determine possible
causative factors; ex
post facto
ex post facto:
Research design in
which researchers
look back in time to
determine possible
causative factors;
retrospective
research design
case-control: A type
of retrospective
study in which
researchers begin
with a group
of people who
already had the
disease; studies
that compare two
groups: those who
have a specific
condition and those
who do not have
the condition
cross-sectional:
Nonexperimental
design used
to gather data
from a group of
subjects at only
one point in time;
study design to
measure exposure
and disease as
each exists in a
population or
representative
sample at one
specific point of
time162 CHAPTER 6 Key Principles of Quantitative Designs