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 webpage was written by Steve Simon on 2002-10-11, edited by Steve Simon, and was last modified on 2008-07-08. This page needs minor revisions. Category: Definitions, Category: Research designs.