Longitudinal Study

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Longitudinal Study Longitudinal study
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This article covers what longitudinal study is, what are its types, the different ways of collecting data for a longitudinal study, as well as its advantages and disadvantages.

What is a longitudinal study?

Longitudinal surveys, on the other hand, involves studying variables for a long period of time and observing the changes in them from time to time. Here, the data is collected from the respondents at the beginning of the study, and then the researcher collects data at different time intervals until the end of the study. Longitudinal surveys are more popularly used in medicinal science to understand and evaluate the effects of medicines, or vaccines, in the long-run on participants. Because longitudinal surveys take place for several years, researchers can establish the sequence of events that may affect the variable under study.

Longitudinal studies involve the use of research surveys in order to collect qualitative or quantitative data. In a longitudinal study, the creator of the survey does not intervene with the participants of the survey. Instead, they distribute the questionnaires over time in order to observe changes in the participants, their behaviour, or attitudes. Most medical studies tend to be longitudinal where the researchers collect data and observe the same participants over several years.

What are the types of longitudinal studies?

Longitudinal studies tend to be versatile, replicable, and they can account for both quantitative and qualitative data. There are three major types of longitudinal studies that can be the basis for future research:

  • Panel Study: A panel study is a type of longitudinal study that examines the same sample over a period of time. Here, the study is conducted at specific intervals for an extended period of time. Most panel studies tend to use quantitative analysis, though, they may sometimes be used to collect qualitative data as well for a qualitative analysis.
  • Cohort Study: In a cohort study, researchers study samples of different cohorts. Cohort studies are most popular in medical research and some even consider clinical trials to be a kind of cohort study. However, in cohort studies, researchers simply observe participants without interfering with the study, while in clinical trials participants do undergo certain tests. 
  • Trend Studies/Analysis: Trend Studies are most common in mass media research. Here, researchers sample different groups of people at different times from the same population and analyse the changes within the groups over a period of time. Example; seeing the shift in people’s attitudes during presidential elections.

What is the Difference Between Cross-sectional and longitudinal studies?

Longitudinal study

Although both cross-sectional and longitudinal research methods are quantitative in nature, there are several differences amongst them. In a cross-sectional study, researchers collect data of a variable at a specific point in time while in a longitudinal study, the data is collected at different times. In longitudinal studies, variables tend to change over time as well. 

Researchers use cross-sectional research to find commonalities between different variables. They use longitudinal studies in order to dissect the findings of the cross-sectional study further. Let’s look at the differences between the two in detail:

Longitudinal studies

Cross-sectional studies

Longitudinal studies take a longer time to be completed, ranging from years to even decades sometimes. 

Cross-sectional studies tend to be less time-consuming and quick to administer. 

Here, the researcher observes participants at different periods in times

Here, the researcher conducts the study over a predetermined specific period of time.

Cause-effect relationship is provided by longitudinal studies.

Cause-effect relationships are not provided by Cross-sectional studies.

Here, only one variable is observed and studied in detail.

Here, different variables are observed at a single point in time.

Longitudinal studies are more expensive and thus, not very accessible to companies and researchers. 

Cross-sectional studies are cost-effective and thus a popular means of study for companies and researchers. 

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What are the advantages and disadvantages of conducting longitudinal surveys?

This section covers the advantages and disadvantages of conducting longitudinal studies:

Advantages of longitudinal studies”

  • Since longitudinal studies allow researchers to follow the participants or subjects in real time, the data collected is highly valuable, enriching, insightful, and valid. This also gives promising and valid results for the study.
  • Longitudinal studies also offer long-term unique and rich data. This is different from cross-sectional studies that only collect short-term data. Longitudinal studies thus permit us to discover long-term relationships between variables.
  • Longitudinal studies also help researchers to uncover and analyse trends from the collected data in real time whether it is a medical study, psychological or a sociological study. 
  • Longitudinal studies allow researchers to observe the variables in the same sample over a period of time. Thus, any changes in the variable can be correctly attributed to the individual.
  • Longitudinal study surveys are flexible as well since it is a long-term study.  
  • Longitudinal studies also eliminate the risk of bias because the researchers are observing and collecting the data in real time.


    Disadvantages of longitudinal studies
  • The main disadvantage of longitudinal studies is that it is unpredictable. Since researchers plan to study the same number of people over time, the drop out rate of participants can also be high and the previously collected data will be useless.
  • Longitudinal studies are time-consuming and costly. It requires a large amount of commitment as well as resources on the part of the researcher.
  • Longitudinal studies also take time to uncover relationships between variables. Moreover any unpredictable event in the natural world can lead to changes in the variables instead of individual factors and hamper the study.
  • Longitudinal studies require large amounts of samples for the study to yield meaningful patterns and insights.

The advantages show us the enormous value of longitudinal studies have to offer, and the disadvantages tell us how to properly plan and execute longitudinal studies to avoid errors and potential biases.

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