StATS: What is a longitudinal design?
A research design where subjects are assessed at several different times
in their lives. Usually, you use this design when you are interested in how
subjects change over time. These studies are often expensive, difficult to
conduct, and have lots of trouble without drop outs. They also will require
more complex statistical analyses. But they provide a wealth of information
that could not be obtained readily with other types of research designs. Here
are two examples of longitudinal designs.
- In Phillips et al (BMJ 2001 Mar 31;322(7289):771), the researchers
studied 3577 men born at the Helsinki University Central Hospital, Finland,
during 1924-33. They collected data at birth on gestational age, birth
weight, and head circumference. They also measured their weight at 15 years,
and their marital status and socioeconomic status as adults. This
longitudinal study came up with the surprising conclusion that men who were
small at birth were less likely to be married as adults.
- In Kivipelto et al (BMJ 2001 Jun 16;322(7300):1447-51), the researchers
re-contacted patients in 1998 who had originally be assessed as part of a
different study in either 1972, 1977, 1982, or 1987. They assesses whether
the patients had signs of Alzhiemers disease in 1998 and correlated this
with their blood pressure and cholesterol measurements at the earlier time.
This longitudinal study showed that high levels of systolic blood pressure
and high levels of cholesterol at mid-life were associated with increased
risk of Alzheimers disease later in life.
This page was written by
Steve Simon while working at Children's Mercy Hospital. Although I do not hold the copyright for this material, I am reproducing it here as a service, as it is no longer available on the Children's Mercy Hospital website. Need more
information? I have a page with general help
resources. You can also browse for pages similar to this one at Category: Definitions,
Category: Research designs.