and effect using cross-sectional designs. For example, a researcher is studying
the effect of self-efficacy on condom use in adolescents. If a cross-sectional
design is used, it would be difficult to determine whether increased self-efficacy
caused increased condom use or increased condom use resulted in a sense of
increased self-efficacy.
Use of a strong theoretical framework can guide the researcher when
speculating about the relationships of the variables being studied with
a cross-sectional design. It is important not to confuse cross-sectional
studies with other designs. For example, a researcher who is interested in
subjects’ cardiovascular responses to stress may start by measuring blood
pressures, exposing subjects to a stressful video clip, and then remeasuring
blood pressures during and immediately after the video. Although data are
collected in the immediate present, data about the IV and DV are not collected
at the same point in time. Therefore, this is an example of an experimental
design rather than a cross-sectional design.
Cohort comparison studies are a specific type of nonexperimental cross-
sectional design where more than one group of subjects is studied at the same
point in time. Cohort comparison designs allow researchers to draw conclu-
sions about variables over time even though data were collected at only one
point in time. In the example of condom use, a cohort design could be used
to study the factors associated with condom use among high school freshmen
as well as high school sophomores, juniors, and seniors. The variables related
to condom use in each group could be analyzed and compared to see if the
same variables applied across the groups or to find out at which grade level
the variables changed. Because following the same subjects as they progress
through high school would take 4 years, gathering data from different subjects
at each grade saves time. The advantages of cross-sectional designs are that they
are easier to manage and are more economical. Because data are collected only
one time from each subject, the threats of mortality, maturation, and testing
are minimized. A limitation of cross-sectional designs is that it is difficult for
researchers to make claims about cause and effect.
Longitudinal Designs
Longitudinal designs are used to gather data about subjects at more than one
point in time. These may be either experimental or nonexperimental designs.
Longitudinal designs are sometimes called prospective designs, which are stud-
ies that begin in the present and end in the future. Nonexperimental, prospec-
tive designs are commonly used in epidemiological studies where researchers
begin by identifying presumed causes and then follow subjects into the future
to determine whether the hypothesized effects actually occur.
KEY TERMS
cohort comparison:
Nonexperimental
cross-sectional
design in which
more than one
group is studied at
the same time so
that conclusions
about a variable
over time can be
drawn without
spending as much
time
longitudinal
designs: Designs
used to gather data
about subjects at
more than one
point in time
prospective
designs: Studies
over time with
presumed causes
that follow subjects
to determine
whether the
hypothesized
effects actually
occur6.3 Categorizing Designs According to Time 163