longitudinal study

Longitudinal Study: Definition and Explanation

Longitudinal study is an observational study that employs continuous or repeated measures to follow particular individuals over prolonged period of time often years or decades. Longitudinal study collects data that is either qualitative or quantitative in nature. In longitudinal study a survey creator is not interfering with survey respondents. Survey respondents are observed over a period of time ranging from months to even decades to observe any changes in them or their attitude. For example, a researcher wants to find out which disease affects young boys (in the age group of 10-15) then the researcher will observe the individuals over that period of time to collect meaningful data.

Unlike Longitudinal studies, where the variables of the research can change during its long course of study, a cross sectional study is conducted in a single instance with all variables remaining the same throughout the study.

A cross-sectional study may be followed up with a longitudinal study.

Following up from our example above, if the cross-sectional study concludes that there is indeed a disease which affects a certain subset of the initial population used for research, then a longitudinal study can be conducted to research the new aspect.

The distinctive difference between both the studies is the timeline and variable. In cross-sectional study, researcher conducts studies using the same variable and the study is carried out only once. In longitudinal study a researcher conducts study using different variable over a period of time and collecting data based on those studies. For instance, researchers gather  biological, social, lifestyle and economic information of their target audience. Then they study the effect of these factors, both separately and in combination, on the their life.

Many medical studies are longitudinal in nature, here a set of sample or same individuals form a group and observed and studied over years. The purpose of using the same individuals or sample in longitudinal study to observe them study any measurable change over a period of time.

Longitudinal study is not just restricted to the field of science or medicine, it has a tremendous impact in the field of business as well. With longitudinal study, one can measure and compare various business and branding aspects by deploying surveys. Some of the classic examples of surveys that can be used for longitudinal studies are:

  • Market trends and brand awareness: To understand a market trend and brand awareness, market research survey and marketing survey works wonders. Through these surveys, businesses or organizations can know what customers want and what they will discard. This study can be carried over a period of time to understand market trends as they are volatile and tend to keep changing.
  • Product feedback: If a business or a brand has launched a new product and wants to know how is the product doing to the consumers then product feedback surveys can be deployed. Feedback from customers about the product can be collected over an extended period of time. Once the data is collected, businesses or brands can put this feedback into practice.
  • Customer satisfaction: Customer satisfaction survey help organization or businesses to know the level of satisfaction or dissatisfaction amongst their customers. Customer satisfaction can be known for as long as a business or organization wishes. This study too can also go on for years.
  • Employee engagement: In organization or offices, the most important aspect of management is employee engagement, how engaged or disengaged employees are at the workplace. This is a continuous study, where employee engagement survey is deployed to understand the level of their engagement and appropriate feedback is collected and acted on.

Learn more: FREE 300+ survey template and research questionnaires

How to conduct Longitudinal Study – with Examples

A longitudinal study is useful not only in the field of science and medicine but in many other fields. There are many reasons why a researcher might want to conduct a longitudinal study. One of the important reasons is, longitudinal studies give unique insights that many other types of research fail.

Let us take an example to understand how to conduct a longitudinal study.

1. Hypothetically, consider that there is a study conducted to understand the similarities or differences between identical twins that are brought up together versus identical twins that were not brought up together on a variety of variables. Researchers, in this case, would want to observe these participants from childhood to adulthood understand how growing up in different environment influences traits, habits, and personality. Since the participants share the same genes, it is assumed that any differences are due to environmental factors. Longitudinal study takes place over a longer period of time ranging from a few years to even decades, data collected through this study can be extremely useful when looking at changes over a period of time. Researchers collect and analyze this draw inferences.

2. Another example is, a researcher has been hired to study if there is a link between violence and video games usage. A sample for the study is collected and to reduce to amount of interference a large group of participants is collected from a population who play video games. Here the age group is restricted to teenagers (13-19 years). The next step is to record how violent participants in the sample currently are. This creates a baseline for later comparisons. Now the researcher will give a log to each participant to keep a track of how much video games they are playing.

This study can go on for months or even years. During this time researcher can draw comparisons between the before and after behavioral aspects of the participants. Thus, helping maintain a record to understand if there is a link between violence and video games.

Types of Longitudinal Study

There are three major types of longitudinal studies:

  1. Panel study: Panel study is a particular type of longitudinal study in which there is a sample of people from a bigger population and study is conducted at specified intervals for a longer period of time. One of the most important features of the panel study is that data is repeatedly collected from the same sample at a different point in time. Most panel studies are designed for quantitative analysis, however, they can also be used with ease for qualitative data collection and analysis.
  1. Cohort Study: Cohort study is a form of longitudinal study that samples a cohort (a group of people who typically experienced a common event at a given point in time). A cohort study is essentially used in the field of medicine. Some might argue and call clinical trials a form of cohort studies, however, in cohort studies, there is a mere observation of the sample or participants involved in the study, unlike clinical trial.
  1. Retrospective study: Retrospective study makes use of already existing data, that exists because a similar kind of research was conducted previously. While conducting a retrospective study, the researcher uses an administrative database that already exists, pre-existing medical records or one-to-one interview.

Advantages of Longitudinal Study

  • Longitudinal study is used exceptionally because of their ability to identify and relate to events. By conducting this type of study the chronicity of events is identified especially in the field of medicine.
  • Since longitudinal study is carried out over a long period of time, it helps to identify and establish a particular sequence of events.
  • Longitudinal study help provide meaningful insights that might not be possible with other forms of study like cross-sectional and similar studies.
  • Longitudinal study allows researchers to trace development over a longer period of time instead of simply jumping to conclusions.

Disadvantages of Longitudinal Study

  • One of the disadvantages of longitudinal studies is that it is not cost-effective. Since this study can run over a period of time, amount of money that needs to be pumped into conducting this study is fairly high.
  • An extended time period may mean dropouts in the number of respondents. People get bored and chances are they won’t participate until the end of research.
  • Its human psychology, people may start to act differently because they know they are being observed. This is a drawback in terms of the data collected. It won’t remain unbiased.
  • Continuity over years may be little difficult. For example, if the lead researcher of the study retires, the person replacing him/her may or may not have the same rapport. So the outcome of the study would be ambiguous.

Learn more- Cross-sectional study: Definition with Examples