Longitudinal Research

A longitudinal research is a kind of an observational research. In this type of research, researcher follows the same subject (or group of subjects) over a period of time. Data collection in this type of research can take years or even decades.


In a longitudinal study, researcher performs a number of observations of the same subject(s) and collects the data across time. The researcher does not interfere with the subject(s) of study.


The advantage of a longitudinal study is that it can be used to study the changes over time. It allows researchers to observe changes in the characteristics of the target population. As the longitudinal study is carried out for a long span, it can be helpful in creating sequences of events.


The main use of longitudinal research is to study the development and natural history of events in the life course. For instance, the researcher can investigate the link between the school failure rates and hostile home environment of the students. The researcher can identify if the students who belong to home with hostile environment are more likely to be failed than those who belong to home with friendly and good environment.



Example of Longitudinal Research


The Framingham Heart Study is a long-term, ongoing cardiovascular longitudinal study which began in 1948 with 5,209 adult subjects from Framingham, Massachusetts, and is now on its third generation of participants. Most of the current knowledge about heart disease, such as the effects of diet, exercise, and common medications such as aspirin, are the outcomes of this study.



Advantages of Longitudinal Research

  • Helps to study the trends in human behaviour

  • Detects the patterns of behavioural change

  • Explains the progression of life events

  • Establishes the sequences of events

  • Establishes the interventions to prevent human and societal ills

  • Tests the theory through the study of causal hypotheses


Disadvantages of Longitudinal Research

  • Time-consuming

  • Can be expensive

  • Participants may leave the study in between

  • Possibilities of practice effects

Types of Longitudinal Research


The different forms of longitudinal research (study) are as follows:


  • Panel study


In this type of study, a fixed sample of subjects are taken and researcher conducts several observations (at different points in time) in them to gather data across the time period.


This study involves follow up with the target population over an extended time period. This study focuses on measuring change over time for the units (e.g., individual) within the population. Unlike cohort studies, panel study extracts sample from the whole and gathers repeated measures from the same set over the period.


Panel study can be used to study the process of demographic change, the dynamics of poverty, flow into and out the child labour market, etc.


Example of Panel study

  • Cohort study

In this type of study, subjects who share a similar life experience or a certain characteristic in a specified time period are studied. A cohort study is a panel study, but a panel study is not always a cohort study because individuals in a panel study do not always share a common characteristic like cohort study.


Cohort study is used to inspect the causes of disease and to determine links between risk factors and health outcomes. “Cohort” represents a group of people who share a common characteristic or experience (e.g., exposure to a drug) within a defined period.


Cohort studies can be prospective as well as retrospective in nature. The main difference between the two is that in case of the prospective study, the study subjects do not have the disease/outcome, however some can have high risk factors while in case of retrospective study, the study subjects already have the disease/outcome.

Example of Cohort study

  • Time-series research


In this type of study, measurements of the same variables are taken at different time points on a group of subjects or other units. Thus, it includes multiple studies on the same variable in different samples over multiple time periods. It is often used to study social trends. That’s why, it is also known as “trend study”. It is different from one-shot cross-sectional study.


Example of Time-series study


Unemployment rates by months in a particular country, graduation rate by year in a particular state, etc.


In time series study, the researcher prepares statistical summary of one particular variable or concept by collecting data from one or more subjects at regular intervals.


Snapshot

Longitudinal research is often considered superior to the cross-sectional study because it provides insight into the details of processes and causes of change within subject and among subjects.


To study the long-term effects of something such as implementation of new study method, intervention of new medication, researcher prefers to do longitudinal studies. Longitudinal studies provide large volume of data to study.


However, these studies can be expensive and time-consuming. Due to long duration of study, some of the team members of research may discontinue for the study. As these studies keep the research topic narrow, they may limit the generalizability of the results.