In panel designs, the same subjects are used to provide data at multiple
points in time. The observational study component of the well-known Women’s
Health Initiative (WHI) is an example of a prospective, nonexperimental, panel
design (National Heart, Lung, and Blood Institute [NHLBI], 2010). In the WHI,
researchers funded by the NHLBI gathered data over an 8-year period from
postmenopausal women between 50 and 79 years of age. The purpose of the
study was to determine reliable estimates of the extent to which known risk
factors predict heart disease, cancer, and fractures in older women. Women
who joined the panel study were asked at different points in time to provide
data about their health behaviors. They were not required to change any of
their health habits—only to report them.
Tr e n d studies use nonexperimental designs to gather data about the vari-
ables of interest from different samples from the target population across time.
An example of this is the Youth Risk Behavior Surveillance System (YRBSS)
conducted by the Centers for Disease Control and Prevention (http://www
.cdc.gov/HealthyYouth/yrbs). Since 1992, the YRBSS has surveyed represen-
tative samples of students in grades 9–12. Repeated every 2 years, surveys
provide data regarding the prevalence of risk behaviors among high school
students. By using different samples of teens, researchers are able to determine
whether the rates of risky behaviors are increasing, decreasing, or staying the
same over time.
Another type of longitudinal design is the follow-up study. Researchers use
this design to follow subjects into the future. These may be either experimental
or nonexperimental designs. Nonexperimental follow-up studies differ from
panel studies in that the samples are not drawn from the general population (e.g.,
not from all postmenopausal women or all teens in high school), but instead
samples are selected because they have a specific characteristic or condition
that researchers are interested in studying. An example of a nonexperimental
follow-up design is a study involving the breastfeeding behaviors of new moth-
ers. The researcher would select a sample of new mothers and follow them for
a period of months to determine variables associated with their continuing or
discontinuing breastfeeding.
Follow-up studies may also be experimental in design. A researcher may
design a supportive educational intervention to increase new mothers’ confi-
dence in breastfeeding. The researcher would randomly
assign mothers to either the new educational intervention
group or the standard of care group. Mothers would be
followed over the next few months to determine whether
the educational intervention made a difference in the
length of time that mothers breastfed their infants. TheFYI
Several research designs allow researchers
to track data over time. These include retro-
spective designs and longitudinal designs.KEY TERMS
panel design:
Longitudinal design
where the same
subjects, drawn
from the general
population, provide
data at multiple
points in time
trend: A type of
longitudinal design
to gather data from
different samples
across time
follow-up: A
longitudinal design
used to follow
subjects, selected
for a specific
characteristic or
condition, into the
future164 CHAPTER 6 Key Principles of Quantitative Designs