Dear Sunds,

I am not sure if I understood the second paragraph of you question. But I see that our question has to with methods often used in developmental psychology.

I hope that what follows can help you to tackle problem.

As far as I know, longitudinal, cross-sectional, and time-lag studies or designs are the main methods used in developmental research. These methods differ in several respects.

Longitudinal studies (LS), cross-sectional (CS), and time-lag (TL) studies are different in terms of goals and procedure. LS are interested in getting access to intraindividual change over time; CS are interested in getting access to inter-ndividual differences at a given point of individuals' development. TL are interested in associating a certain age with a certain developing capacity, for example.

Even though both longitudinal and cross-sectional studies are often used in developmental psychology, only the former is consistent with the very nature of developmental psychology, to get access to intra-individual change over time.

Let us suppose that you have a sample of, say, 100 individuals who were born in the same year, 2000, for example, and that you are interested in seeing if their cognitive development changes over time. In order to attain this goal, you have to evaluate your sample' cognitive abilities, for example, at T1 (2018), T2 (2020), T3 (2022), and so forth, when they are eighteen, twenty, and twenty-two-year olds, respectively. So, in a longitudinal design, individuals of a certain age, 10-year-olds, for instance, at T1, are followed and evaluated when they are 12-year-olds (T2), 14-year-olds (T3), and so forth. Thus, you have repeated evaluations (at T1, T2, T3, and so forth) of the same individuals of a given cohort (e.g., those individuals who were born, for example, in 2000) over time. Needless to say, the more a longitudinal study is long, the more likely you are to lose some individuals of the initial sample.

In contradistinction, in a cross-sectional design, you have individuals of different ages (e.g. 10, 12, 14- year olds) who are evaluated at the same time (at T1, for example). In a nutshell, in longitudinal studies, individuals who belong to a certain cohort or have the same age are assessed at several points in their development (at T1, T2, T3, and so forth). In cross-sectional studies, individuals of different ages (e.g., 10, 12, 14- years olds) are assessed only once (at T1, for example).

In a time-lag design, you can see, for example, if a given cognitive performance on a Piagetian task (e., a proportionality task) is present, for instance, when individuals are 18 year-olds. In a time-lag design, however, these individuals have to belong to different cohorts and be assessed at different times.

In multi-wave studies, you still have three types of developmental studies or designs, longitudinal sequential studies, cross-sectional sequential designs and time-lag sequential designs. Each of these types allows you to make longitudinal, cross-sectional, and time-lag evaluations. In the first type, you follow different cohorts over a certain period of time; in the second, you assess a cross-sectional sample at different times (T1, T2, T3, and so forth); In the third, you assess a time-lag sample at different times. For a more detailed description of these methods you can read, for example, the following book; Achenbach, T (1978). Research in developmental psychology: Concepts, strategies and methods. New York: The Free Press.

I hope that i have got your question and that this hepls.

Best regards.

Orlando

Check this link

https://www.google.com/amp/s/www.researchgate.net/post/What_are_the_differences_between_cross-sectional_and_longitudinal_studies/amp

regards

this link is useful

https://www.sciencedirect.com/science/article/.../S000187911300173... -

regards

Thank you for your replies.