Some fields in psychology are interested in looking at the long-term effects of certain phenomena. Developmental psychology, for example, focuses on explaining how humans develop over time. For instance, Piaget theorised the four stages of development, but how were these investigated in research?
A specific research study needs to be applied to test for the changes across time of certain psychological features - longitudinal research.
- This explanation will introduce you to longitudinal research studies.
- Secondly, the explanation will apply longitudinal research to psychology.
- Moving on from this, we will explore how longitudinal research designs
- Then a longitudinal research example will be given.
- Lastly, the strengths and weaknesses of longitudinal research will be summarised.
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.
Longitudinal research refers to a research method in which individuals are tested over a long period. The period in which participants are tested can range from months to years.
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:
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.
Researchers may be interested in studying how intelligence quotient may change with age. To study this, they may define three cohorts and compare them.
The cohorts or groups could emerge based on age. For example, cohort one could include those aged 10-20 years, the second cohort could include participants aged 21-40 years and the third cohort could consist of those aged 41-60 years.
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.
Meaning the process is naturally occurring.
An example of a longitudinal cohort retrospective study is that it could investigate the effects of prenatal exposure to alcohol and later alcohol dependency.
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.
The 1970 British Cohort Study is an example of a longitudinal cohort prospective study. The study followed the lives of around 17,500 participants born in the same week in England and Wales.
No clear aim was defined for the study back in 1970, but different hypotheses have been tested throughout the years using the data collected.
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.
The research aim and hypothesis will determine the parameters the participants need to fulfil. In the case of the example above, one of the parameters would be that participants had reading difficulties in childhood.
Secondly, researchers decide how and what type of data they will be collecting, which is influenced by what approach the longitudinal research takes:
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.
An example of longitudinal research is research investigating the effects of maternal deprivation on later relationships. The hypothetical aim of the study is to identify if the adverse effects of maternal deprivation are long-lasting over time.
The researchers may decide to collect data from questionnaires, interviews, and psychometric tests from all participants every two years over ten years.
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.
Suppose a longitudinal cohort study identifies that people living in a certain area have lower IQ scores than others. In that case, further investigation may be done to identify if policies in that region are causing inequality in access to education and achievements.
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.
For example, researchers can identify whether the quality of attachments formed with a primary caregiver affects later relationships or determine if pharmacology and cognitive behavioural therapy are effective interventions.
The weaknesses of longitudinal research are:
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.
Longitudinal Research - Key Takeaways
- Longitudinal research is used when researchers want to test the same participants for a long time. This method usually collects data from participants at regular intervals throughout the investigation.
- The importance of longitudinal research in psychology is that it can help researchers see the long-term effects of medication and intervention, learn about the order of events that happen over time, and recognise changes that occur over time.
- They are different types of longitudinal research: a Cohort study and a Panel study.
- The strengths of longitudinal research are there is less likelihood of recall bias affecting the study results. It can also provide detailed information that may not be able to be found in a short time. It also can help researchers identify what they should research and investigate further. It also has economic and social benefits.
- The weaknesses of longitudinal research are that it is time-consuming and expensive, a large sample is needed for the findings to be meaningful, and there is a high chance that participants will drop out.
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