Why would researchers want to conduct studies that take a very long time to complete? A longitudinal study can be used to discover relationships between variables that are not related to various background variables. This observational research technique involves studying the same group of individuals over an extended period.
Data is first collected at the outset of the study, and may then be repeatedly gathered throughout the length of the study. Doing this also allows researchers to observe how variables may change over time.
For example, imagine that a group of researchers is interested in studying how exercise during middle age might impact cognitive health as people age. The researchers hypothesize that people who are more physically fit in their 40s and 50s will be less likely to experience cognitive declines in their 70s and 80s.
The researchers recruit a group of participants who are in their mid-40s to early 50s. They collect data related to how physically fit the participants are, how often they work out, and how well they do on cognitive performance tests. Periodically over the course of the study, the researchers collect the same types of data from the participants to track activity levels and mental performance.
Longitudinal studies are usually observational in nature, and are a type of correlational research. Longitudinal research is often contrasted with cross-sectional research. While longitudinal research involves collecting data over an extended period of time, cross-sectional research involves collecting data at a single point in time.
Types of Longitudinal Research
There are three major types of longitudinal studies:
- Panel study: Involves sampling a cross-section of individuals.
- Cohort study: Involves selecting a group based on a specific event such as birth, geographic location, or historical experience.
- Retrospective study: Involves looking to the past by looking at historical information such as medical records.
For many types of research, longitudinal studies provide unique insight that might not be possible any other way. This method allows researchers to look at changes over time.
Because of this, longitudinal methods are particularly useful when studying development and lifespan issues. Researchers can look at how certain things may change at different points in life and explore some of the reasons why these developmental shifts take place.1
For example, consider longitudinal studies that looked at how identical twins reared together versus those reared apart differ on a variety of variables. Researchers tracked participants from childhood into adulthood to look at how growing up in a different environment influences things such as personality and achievement.
Since the participants share the same genetics, it is assumed that any differences are due to environmental factors. Researchers can then look at what the participants have in common versus where they differ to see which characteristics are more strongly influenced by either genetics or experience. Note that adoption agencies no longer separate twins, so such studies are unlikely today, and longitudinal studies on twins have shifted to those within the same household.
Because longitudinal studies take place over a period of years (or even decades), researchers can utilize their data to establish a sequence of events when looking at the aging process.
As with other types of psychology research, longitudinal studies have strengths and weaknesses. There are some important advantages to conducting longitudinal research, but there are also a number of drawbacks that need to be considered.
Longitudinal Studies Can Be Expensive
Longitudinal studies require enormous amounts of time and are often quite expensive. Because of this, these studies often have only a small group of subjects, which makes it difficult to apply the results to a larger population.
Participants Tend to Drop Out Over Time
Another problem is that participants sometimes drop out of the study, shrinking the sample size and decreasing the amount of data collected. This tendency is known as selective attrition. Participants might drop out for a number of reasons, like moving away from the area, illness, or simply losing the motivation to participate.
In some cases, this can influence the results of the longitudinal study. If the final group no longer reflects the original representative sample, attrition can threaten the validity of the experiment. Validity refers to whether or not a test or experiment accurately measures what it claims to measure. If the final group of participants is not a representative sample, it is difficult to generalize the results to the rest of the population.
The World’s Longest-Running Longitudinal Study
The Genetic Studies of Genius, today referred to as the Terman Study of the Gifted, was originally started in 1921 by psychologist Lewis Terman. He aimed to investigate how highly intelligent children developed into adulthood. Results were still being compiled into the 2000s.
A Word From YoStatistician Consultancy
A longitudinal study can provide a wealth of information on a topic. Such studies can be expensive, costly, and difficult to carry out, but the information obtained from such research can be very valuable.
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