Longitudinal studies: what are they and how do they work in research?

A type of research widely used to study the evolution of social and natural phenomena.

Longitudinal studies are a research method that consists of measuring a phenomenon over a given time interval. In this sense, they are used to analyze and observe the evolution of a phenomenon or its elements in a sequential manner. They are frequently used in research related to health sciences, as well as in statistics, psychology, sociology and education.

In this article we will see what a longitudinal study is, and what are some of its characteristics.and what are some of its main characteristics and uses.

What is a longitudinal study and what is it for?

Longitudinal studies are a research methodAs such, it is a structured set of procedures that allows us to obtain information on a given topic.

Specifically, the objective of longitudinal studies is to obtain information on a process of change. information about a process of change.. They also serve to estimate incidences and anticipate risks. This can occur through the observation and measurement of individual patterns and their stability or modifications over time.

In other words, they allow estimates of the rate of change as a function of time, and in relation to different characteristics of the individual such as age or other conditions (Arnau and Bono, 2008).

In this sense, longitudinal studies have traditionally been considered as the opposite of cross-sectional studies (Arnau and Bono, 2008). as opposed to cross-sectional studiesThe scientific method is based on momentary or fixed observations at a specific point in time, although they are not unrelated to each other.

Disciplines that use it and related studies

Longitudinal studies are particularly used in the health sciences, but they also make it possible to to measure the evolution of certain phenomena in psychology, education, sociology and demography, to name a few.to name but a few.

In turn, the term "longitudinal study" may have some variations according to the specific discipline that uses it. For example, when it comes to studies conducted in the field of sociology, longitudinal studies are related to a type of study called "panel study"; while when it comes to studies in the epidemiological and demographic field, it is a subtype of the classic cohort study (those that measure the elements of a phenomenon between two or more time intervals).

In relation to the above, another type of cohort study are life tables. The difference between a life table and a longitudinal study is that the former performs a measurement considering only the beginning and the end of the interval (i.e., the phenomenon is observed twice, once at the beginning and once at the end, and the data are analyzed from there). In contrast, in the longitudinal study measurements are made repeatedly (Delgado, M. and L. (Delgado, M. and Llorca, J., 2004).

Likewise, when it comes to studies that are applied in the statistical field, they have also been considered as a type of study of repeated measurements. They are so called because they are a type of study based on repetitive measurement, i.e., they make it possible to observe a certain number of occurrences of the phenomenon or of some of its characteristics in a specific time.

Types of longitudinal research

Depending on the specific field in which the longitudinal study is applied, it can be of different types. For example, we will briefly describe its characteristics in epidemiology and statistics.

1. In epidemiology

The basis of the longitudinal study used in epidemiology is to know the disease experience of a population over time. They allow transitions between health and disease states, and to incorporate variables such as age or gender.and incorporate variables such as age or gender.

2. In statistics

This is a study that consists of more than two measurements over a period of time.. In other words, it is not only a matter of measuring one phenomenon at the beginning and another at the end, but of making repeated measurements of the phenomenon. In turn, it can be applied in different fields, for example in developmental psychology.

Design of this form of research

As with all research methods, longitudinal studies are applied according to the specific objective pursued by the research. The description of the studies and the elements that make them up and that will allow them to be carried out, is what we know as the research design.

The design of a study is important because it it ensures that the methodology will correspond to the objectives and will make it possible to arrive at consistent results. and will make it possible to arrive at results that are consistent with them. In this case, longitudinal studies are used in research that aims to understand a process of change over time.

Although the specific design depends on the type of longitudinal study to be conducted, as well as the specific field of application, broadly speaking this type of research requires including the following elements:

• Longitudinal data, which are The number of repetitions in which the phenomenon will be observed..
• Observed elements, which can be units, individuals, subjects, groups, populations.
• Time points, which are the time intervals in which the element is recorded, ranging from a few minutes to several years.
• Response profilealso called trend or curve, which is the response set of the measured unit.

Limitations

In longitudinal studies, as in other studies based on repeated measures, there are two fundamental implications. there is a dependence between the number of times the phenomenon is repeated and the observed unit of measurement.. That is, the number of repetitions is the main criterion for explaining the phenomenon under study.

The second is that the circumstances or variable under which the phenomenon may be repeated are often beyond the control of the researcher. are beyond the control of the person doing the researchThe second is that the circumstances or variable under which the phenomenon may be repeated are often beyond the control of the researcher, so that the data may often be incomplete.

Bibliographical references:

• Arnau, J. and Bono, R. (2008). Longitudinal studies of repeated measures. Design and analysis models. Escritos de Psicología, 2(1): 32-41.
• Delgado, M. and Llorca, J. (2004). Longitudinal studies: concept and particularities. Revista Española de Salud Pública, 78: 141-148.