Beyond snapshots: Understanding development over time
Why do some early life experiences seem to shape people for decades, while others appear to fade over time? Why does the same life event have a major impact on one child but little effect on another? In order to understand which factors have a profound influence on development, researchers from different disciplines follow the same individuals over many years. Moritz Daum, Nora Raschle, Michael Shanahan, and Doris Hanappi share insights from longitudinal research across psychology, neuroscience, sociology, and education policy.
Why snapshots are not enough
Understanding development requires looking beyond single moments in time. Many studies compare children of different ages at a single point: an approach known as “cross-sectional research.” While this can often reveal differences between age groups, it provides only a limited picture of how individual development takes place.
Moritz Daum is a Professor of Developmental Psychology and the Director of the Jacobs Center for Productive Youth Development. He illustrates the shortcomings of this approach by quoting Developmental Psychologist Karen Adolph: “Cross-sectional studies leave researchers with a gallery of before-and-after snapshots, studio portraits of newborns, and fossilized milestones, but little understanding of the process of development itself.” To move beyond these snapshots, researchers rely on longitudinal studies that follow the same individuals over many years. Through repeated observations of the same people, they trace developmental trajectories and detect how early experiences can impact the later life of individuals. As Nora Raschle, Professor of Developmental Neuroscience, states, “If you study development, you have to study change over time.”
Michael Shanahan, Professor of Sociology, adds another important dimension. Understanding development requires looking not only at changes within individuals. “It’s not just people who are developing,” he explains, “they are developing in a possibly changing environment.”
Historical events, as well as changes within social institutions, can influence these developmental pathways, he notes. “The way schools are structured and the different ages at which transitions occur are all very important.”
Small influences, long-term effects
Development is often associated with major life events such as parental divorce, moving to a new city, or serious illness. Longitudinal studies reveal that development is shaped not only by these dramatic life events but also by smaller influences that accumulate over time. Even though major events can have a significant impact on children, their effects tend to be overestimated.
Shanahan questions the idea that major life events determine developmental outcomes. “The extreme impact of major events is a bit of a myth,” he explains. “It’s what people are bringing to these situations.” People differ in how they respond to difficult experiences. As Shanahan notes, “some people are just better positioned to handle events – for example, those who have a higher cognitive capacity or self-control, or are better educated and wealthier.” Hanappi, who leads the Swiss EdLab at the Jacobs Center, illustrates this with the example of parental divorce. “Some children cope more easily with their parents’ divorce,” she explains. Others, however, may struggle more. These differences among children often depend on previous events and conditions. “If they have experienced chronic stress within their parental relationship, for example,” she observes, “it becomes more difficult for them to cope later on.”
Another aspect of development that is often overlooked concerns transitions that fail to occur. “Sometimes the most important transitions are the ones that don’t happen,” Hanappi explains. In life course research, these so-called “non-transitions” can shape developmental trajectories just as strongly as major life transitions. “Examples include never entering high school, never entering the labor market, or never forming a partnership,” she says. Such developments are difficult to measure because they often remain invisible for a long time. With longitudinal data, however, researchers have what Hanappi describes as “the privilege of waiting.”
By following individuals over extended periods, they can observe whether such transitions eventually occur. In some cases, what initially appears to be a non-transition may turn out to be one that happens with a delay. Additionally, the indirect impact of non-transitions on other areas in life only becomes visible much later. Daum refers to what researchers sometimes call “sleeper effects,” situations in which early experiences appear to have little immediate impact but influence development years later.
Longitudinal studies can also reveal patterns that are invisible in shorter studies. Daum points to one of his current research projects on children born slightly preterm as an example. Although premature birth is often associated with developmental risks, long-term observations show surprisingly small differences in communicative development later in life. One possible explanation, he suggests, is that children born slightly earlier are also exposed earlier to communicative input from their environment – from parents, siblings, and their environment. This earlier exposure may partly compensate for initial disadvantages.
Studying a changing world
Longitudinal studies are particularly important when new social phenomena emerge. Digital technologies, for example, raise many questions about how media use might shape development across the lifespan. Yet answering these questions in real time is not always easy. As Raschle explains, researchers often face a simple limitation: The necessary data may not yet exist.
“If we say that longitudinal research takes a lifespan, and we want to understand the impact of media across that lifespan,” she notes, “we simply haven’t studied it yet.” Many digital technologies, such as artificial intelligence, are relatively new, making long-term observations essential for understanding their potential influence on development.
Despite the scientific value of longitudinal studies, conducting them is often difficult in practice. Following individuals over many years requires sustained cooperation from participants, institutions, and families. One major challenge is that participants do not remain in studies forever. Raschle points out that dropout is rarely random. “Nothing happens at random,” she explains. Over time, certain groups are more likely to leave studies than others, which can make it harder to interpret the results. Longitudinal studies therefore face obstacles. Besides the risk that participants may drop out over time, access to research fields can be restricted by institutional gatekeepers, particularly in educational settings in which researchers depend on the cooperation of schools and administrators.
At the Jacobs Center, researchers address these challenges in several ways. Dropouts, for example, are not treated simply as missing data but as potentially informative, because understanding which groups leave studies and why can offer important insights into social inequalities and developmental trajectories. Researchers at the Jacobs Center also build close collaborations with schools, institutions, and participating families to create the trust necessary for conducting long-term longitudinal research.
Author: Hanane Oubari
Editor: Sandro Fässler
