Longitudinal studies: what do they consist of?

Longitudinal studies They allow observations to be made, in a sequenced manner, of the transformation or evolution of the phenomenon being studied.. They are widely used in various fields of knowledge, such as medicine, psychology or sociology.

This type of study requires monitoring of the variables that are being analyzed. The duration is determined by the researcher and they can last weeks, months, years and even decades.

What is a longitudinal study?

Longitudinal studies are a type of observational (non-experimental) design that analyzes the changes of certain categories, concepts, events, variables, contexts or communities over time. This design collects data at different moments or time intervals in order to make inferences regarding the evolution of what was studied, its determinants and consequences (Hernández-Sampieri, Fernández and Baptista, 2014).

Other authors, such as Visser (as cited in Arnau and Bono, 2008), state that a longitudinal study consists of examining the changes that occur, over time, in the same sample of subjects and verify interindividual differences in intraindividual changes. That is, they study the processes of change directly associated with the passage of time (Arnau and Bono, 2008).

It is also understood as a research design that studies and evaluates the same people over a period of time (Myers, 2006). The central idea of ​​all these definitions is not the number of variables studied, whether it is one or several; whether they are people, phenomena or communities, The central idea is in time, in the evolution and in the respective changes of the object of research. For example:

To analyze the changes in attitude towards euthanasia over a period of ten years in an urban community. To study the relationship between physical activity and aging in a sample of 40-year-old people over a period of five years. To observe how develops a peasant community over the years, with the arrival of the internet into their lives.

Characteristics of the longitudinal study

The main characteristic, as previously stated, is that Data collection is carried out at various times. Unlike cross-sectional designs, where data is collected at a single moment, in longitudinal designs it is collected at several times. This form of collection distributed over time allows us to identify changes.

Observations are always made on the same object of study, whether it is a phenomenon, community or person.. It is important that the sample be the same at all times. Obviously, this may change over time, since change is a vital constant. What is sought, exactly, is that the sample be maintained every time a measurement or observation is made.

Another characteristic of longitudinal studies is that allow the researcher to capture intra-individual or intra-group differences. As the main objective of this type of design is to observe the evolution and change that the study variables have had during a certain period, the respective variations that have occurred in the sample are analyzed.

Finally, based on the objectives of the longitudinal data analysis of Arnau and Bono (2008), it can be stated that another characteristic of these designs is that they provide information on interindividual differences, on the relationship between intra- and interindividual changes and on the variables that influence its variations.

Types of longitudinal studies

Longitudinal designs are divided into three types: trend designs, evolutionary group analysis designs (cohort) and panel designs.

Longitudinal trend studies

Trend designs analyze changes over time in categories, concepts, variables or their relationships in a general population (Hernández-Sampieri, Fernández and Baptista, 2014).

The central characteristic of this design is that it focuses exclusively on the population or universe and not on the samples. For example, carry out a study to analyze the change in perception about abortion among university students in a city.

Longitudinal cohort studies

Unlike the trend design, cohort designs They examine changes in specific subpopulations or groups. Their attention is focused on groups of individuals with a common characteristic.

These designs track groups over time and typically draw a sample each time data is collected on the group or subpopulation—rather than including the entire subpopulation (Hernández-Sampieri, Fernández, and Baptista, 2014). It is important to note that, although the sample can be changed, it is not configured with elements that do not belong to the group or subpopulation studied.

Longitudinal panel studies

Panel layouts are similar to cohort and trend layouts, only the same cases or participants are measured or observed at all times or moments.

For example, observe a group of depressed patients monthly (for a year) to analyze whether their positive expectations of the future increase and whether their negative expectations decrease (in each observation the patients would be the same people).

Advantages and disadvantages of longitudinal studies

There are several reasons why a researcher might conduct a longitudinal study and others why they might choose another option. Next, we will analyze the advantages and disadvantages of this type of design.

Advantages

Because the study is carried out over the long term, its authenticity is verified beforehand, this makes the results have higher level of validity.Long-term relationships cannot be discovered in a short-term investigation, but short-term relationships can be monitored in a long-term investigation. This allows for a wider margin to examine the changes and thus better understand the evolution of the variables.The longitudinal design allows you to find trends and relationships within data collected in real time.Researchers have flexibility which is not possible with other research formats.

Disadvantages

The main disadvantage of longitudinal designs is that the research is more likely to provide unpredictable results.It may take a long time before the data begins to produce observable patterns or relationships that can be monitored.It is possible that the initial sample may be lost over time.To develop relationships or patterns, a large amount of data must be collected and extracted.Longitudinal design tends to be more complex and expensive. Requiring more time requires more resources, so it is possible that investment and expenses will increase.

In this article we have talked about a type of study that is frequently used in research when describing changes. With research of this type we have discovered such curious phenomena as, for example, the Flynn effect.

You might be interested…