Longitudinal study

A longitudinal study is a form of research that follows the subject of the study over a certain period. These studies are also known as cohort studies or prospective observational studies. To conduct the study, the researchers select a person or group of people to serve as the study subject. The researchers will keep track of these people and observe them several times over a period of weeks, months, or years. Observation is key; the researchers do not interfere with the subjects they are studying. Instead, they observe some trait or behavior of the subjects over time and compare the results from each observation. This sequence of observations allows the researchers to look for patterns of change and cause-and-effect relationships. Such studies are useful for many purposes, including determining causes of diseases.

Background

The purpose of research is to answer a question. The researcher may want to determine how many people in a particular population have a certain trait, how a disease spreads or develops over time, or the effect a particular habit or behavior has on people. To do this, researchers establish a theory, or hypothesis, about what they think will happen. They then design a study that will gather the information needed to determine if their hypothesis is correct and help determine the answer to the question.

A number of different factors can be considered in designing a research study. The researcher first decides what information is needed to answer the question, and then plans a study that will provide useful results. The study must be free of bias, meaning it cannot be designed in a way that favors one type of results. Study subjects are chosen to provide as accurate a sampling of whatever is being tested as possible; for instance, if someone is testing the effectiveness of a new teaching method, choosing only students who are at the top of the class or only those who are learning disabled will not provide a fair assessment of the teaching method unless the study's purpose is to determine if the teaching method helps these student groups.

Studies also often include a control group to help validate the results of the observation. For instance, in the test of the new teaching method, a group of students with a similar background to those in the test group might be taught the same material with the usual teaching method. This allows researchers to more accurately determine how the new teaching method affects learning.

Researchers also need to determine what type of study will best provide the information they need. In some studies, such as case reports or systematic reviews, researchers use previously gathered information in written form to begin their investigation. In other cases, they might need to use studies done on animals.

In many instances, such as studying how people act or interact and how certain conditions or behaviors affect the development of various diseases, researchers will study human subjects. Some of these studies, such as clinical trials, involve people undergoing certain treatments so researchers can see the outcomes. These can include randomized controlled trials, in which people are randomly assigned to a group, and in which some subjects change their behavior in some way (start exercising, or changing eating habits, for instance).

In many other cases, researchers simply observe what is already going on in the person's life. For instance, if people are exposed to a chemical spill, researchers might observe them to see how their health is affected. There are two main ways to do this. In one method, the cross-sectional method, researchers will observe and gather information one time to see how the people were affected. In the longitudinal method, the observation will take place over several weeks, months, or years to see what, if anything, happens to these people after the exposure.

Overview

In a longitudinal study, people who have something in common are studied over time and compared to those who do not have that same thing in common. Longitudinal refers to something that has a length; in this case, it refers to the fact that the study is done for a length of time. For instance, in the example of people who were exposed to a chemical spill, the group that was exposed will be compared to a control group of people who are similar to the group that was exposed in other ways (age, gender, overall health condition, etc.) except for the chemical exposure.

One of the main strengths of the longitudinal method is it allows researchers to see how the situation with the group changes over time. For instance, people exposed to the chemical might not exhibit any symptoms right away but may develop different health conditions weeks or even years later. Comparing the health conditions developing in the exposed group to the health of those who were not affected can help researchers determine if the chemical spill is a cause.

Longitudinal studies have applications in non-medical situations as well. For instance, researchers might identify groups of children and parents who participate in a mommy-and-me music program, a similar group of children and mothers who take part in a mommy-and-me yoga program, and a third group of mothers and children who do not participate in any mommy-and-me activities together. By gathering information through observation when the subjects are participating in the activities as well as three, five, ten, fifteen, and twenty-five years later, the researchers can determine if early exposure to music enhancement activities affects the child's musical abilities later. The other two groups are control groups to help researchers identify effects related to participation in mommy-and-me activities or the absence of such participation.

This type of study is particularly useful for determining cause-and-effect relationships between a suspected cause and the outcome. It also provides a broader base of information than a single observation, such as that in a cross-sectional study. However, there are limits to longitudinal studies, and they may not take into account all relative variables. For instance, the parents involved in family music classes may have a greater interest in music and expose their children to music in other ways as well.

Bibliography

Caruana, Edward Joseph, et al. "Longitudinal Studies." Journal of Thoracic Disease, Nov. 2015, www.ncbi.nlm.nih.gov/pmc/articles/PMC4669300/. Accessed 27 Apr. 2017.

"Longitudinal Studies." British Medical Journal, www.bmj.com/about-bmj/resources-readers/publications/epidemiology-uninitiated/7-longitudinal-studies. Accessed 27 Apr. 2017.

"Study Design." Unite for Sight, www.uniteforsight.org/research-methodology/module2. Accessed 27 Apr. 2017.

"Types of Study Designs." Georgia State University, research.library.gsu.edu/c.php?g=115595&p=755213. Accessed 27 Apr. 2017.

"Types of Studies." Ebling Library, University of Wisconsin Madison, researchguides.ebling.library.wisc.edu/c.php?g=293229&p=1953448. Accessed 27 Apr. 2017.

"Understanding Research Study Designs." University of Minnesota, hsl.lib.umn.edu/biomed/help/understanding-research-study-designs. Accessed 27 Apr. 2017.

"What Researchers Mean by Cross-Sectional vs. Longitudinal Studies." Institute for Work & Health, www.iwh.on.ca/wrmb/cross-sectional-vs-longitudinal-studies. Accessed 27 Apr. 2017.

"Why Do We Conduct Research?" University of Gronigen, www.ppsw.rug.nl/~bve/stat/module1/1Waarom.html. Accessed 27 Apr. 2017.