Longitudinal Research

Longitudinal Research Study

When conducting research, you may want to discover how something develops over several years. Researchers may ask themselves how occurrences in childhood affect the person in adulthood, for example.

Similarly, pharmaceutical companies can be interested in assessing how certain drugs affect people in the long term. These two research concepts can be investigated via longitudinal studies.

Fig. 1. Picture resembling human ageing and possible testing points in a longitudinal study.

One of the main reasons why longitudinal research is used in psychology is to establish the long-term effects of different phenomena.

In developmental psychology, longitudinal research can support researchers in establishing how a developmental process takes.

Longitudinal research is also widely used when assessing a given therapy type or a specific medication's effects. Generally speaking, longitudinal research is practical when studying changes that occur over time.

Longitudinal Research in Psychology

While the term longitudinal refers to research that investigates processes/phenomena that develop over time, within this form of research method, there are several sub-types.

The different types of longitudinal research used depends on:

• The sample.

Longitudinal Research: Cohort Study

A cohort study is a form of longitudinal research investigating a group of people with common characteristics. Part of the design process of a cohort study involves defining the cohorts that will then be compared.

There are two forms of longitudinal cohort research: retrospective and prospective studies.

Retrospective studies present a sample of participants who have already been exposed to specific phenomena.

As you can infer from the example, the researchers do not actively manipulate the alcohol consumption of pregnant women. Instead, they would look for participants exposed to alcohol prenatally and measure their current alcohol consumption patterns.

Differently, in prospective studies, participants have not experienced the phenomena or outcome but may be vulnerable in some cases to the variables being studied.

Researchers design and start the study before identifying a clear hypothesis to test. The prospective research design could record outcomes in a group with common characteristics.

Longitudinal Research: Panel Study

A panel study is a form of longitudinal research investigating a group of people over a long time. The sample of the study is also called a panel.

The panel is defined at the beginning of the research process and is followed up for a set amount of time.

Panel studies usually investigate people's beliefs, attitudes and opinion changes across time.

Longitudinal Research Design

Designing a longitudinal study is not particularly different from designing other studies. Let's review the steps in the design of a longitudinal study.

First, researchers identify the phenomena they are interested in. In the case of a longitudinal study, it would be something like establishing the effect that reading difficulty in childhood has on career choice in adulthood.

Secondly, researchers decide how and what type of data they will be collecting, which is influenced by what approach the longitudinal research takes:

• Prospective research collects information on something the researcher expects to happen.

• Retrospective research collects information on something that has already happened.

After this has been identified, the researcher establishes the data collection methods they will use. In addition to how frequently and at what time intervals the data will be collected.

To ensure that the research is valid, the researchers need to use the same planned data collection methods and follow the same protocol each time they collect data. They need to record all of the collected data from the research needs.

The final stage of the longitudinal research is analysing and reporting the results.

Longitudinal Research Example in Psychology

A longitudinal research example in psychology is the 1970 British Cohort Study. The study initially started by recruiting over 17,000 babies born in the same week in England, Scotland, Wales, and Northern Ireland. The study collected data from participants of different ages throughout their lives.

The study aimed to identify factors such as policing, individual differences, and mental health and the long-term effects of these across the lifespan. It provided vital information on social mobility, education and opportunities, training, and employment.

The study used a series of methods to collect data, such as:

• Face-to-face interviews (including parent interviews).

• Self-completion questionnaires.

• Cognitive assessments.

• Medical examinations.

• Psychological tests.

• Collecting information concerning educational information.

  The study used primary and secondary sources to collect data.

From this research, psychologists can learn about the long-term effects of certain traits, illnesses or experiences. Researchers can also use this to identify what factors should be investigated in experimental conditions.

Longitudinal Research Strengths and Weaknesses

The strengths of longitudinal research are the following:

• It allows researchers to identify how time affects a phenomenon, specifically ones that affect important social variables such as the economy, education, and general welfare.

• Longitudinal studies are large-scale studies. Researchers can identify many variables that may affect the subject the researcher is interested in. Therefore, longitudinal research provides detailed information about a phenomenon.

• Findings from longitudinal factors can help researchers identify what phenomenons need to be tested empirically in experimental conditions to learn more about the causes.

The weaknesses of longitudinal research are:

• As it is a time-consuming type of research, it is often quite costly and difficult because it uses multiple methods to collect data.

• Researchers need to recruit a large sample when conducting longitudinal research. If not, it is difficult to infer if patterns and findings of results are meaningful, leading to non-generalisable results.

• As the research takes over a long period, participants are more likely to drop out. When this happens, it isn't easy to compare the results across the study time points, affecting the reliability and validity of the study.