Joran Jongerling has been working as a statistician in the Department of Methodology and Statistics at Tilburg School of Social and Behavioral Sciences since July 2021. He received his PhD from the University of Utrecht on the analysis of intensive longitudinal data and his focus is still largely on this type of analysis. Besides research with intensive longitudinal data, Joran teaches students at Tilburg University. Together with Eeske van Roekel (Developmental Psychology) he is the director of the Tilburg Experience Sampling Center (TESC). Sandra (TESC project manager) talks to Joran about his interest in intensive longitudinal data, his career, and about challenges and developments in the fast-growing field of intensive longitudinal data analyses.

Intensive longitudinal data

If you are not familiar with the term yet, an explanation is in order. Joran explains briefly and simply what intensive longitudinal data is. “If you measure people very often and the measurements are close together, then you are dealing with intensive longitudinal data. What is a lot and what is close together? No one agrees on that, so everyone can put their own interpretation on it. It usually comes down to measuring the same people several times a day.” The Experience Sampling Method (ESM), also called Ecological Momentary Assessment (EMA), is the intensive longitudinal research method that generates this data. Participants report on thoughts, feelings, behavior, or environment at multiple moments. They do so at the moment itself or shortly after. Joran is involved in statistics of intensive longitudinal data. He started his career as a PhD researcher in Utrecht with Ellen Hamaker.

By chance in statistics

In his own words, it was partly by chance that he started studying statistics and earned his PhD on intensive longitudinal data. Joran studied neuropsychology, got his Master’s, and applied for a research project at the University of Amsterdam. “The requirement was that everyone who was going to do research had experience with statistics. I didn’t have that experience, so I started studying statistics. After that, the plan was that I would go back to psychology, but the latter simply never happened.” Joran liked statistics so much, that, when he got the offer to do a PhD focusing on intensive longitudinal data with Ellen Hamaker in Utrecht, he made the choice quickly.

More and more questions

During his PhD research, Joran focused on autoregressive (AR) models. Joran talks about this type of model, “The idea is that you measure people very often and that you expect their scores to fluctuate a bit, but not to change systematically. Suppose you look at how cheerful I am. Some days I’m more cheerful than others, but my baseline level is fairly stable. It doesn’t increase weeks after week. In autoregressive models, you see variation around a stable level and no systematic changes.” During his PhD research, Joran explored methods to estimate the development of multiple people at once, how to look at differences between people, and at what these differences meant. Joran explains how more and more got added to these core questions, such as: “How can we study people’s development if you look at multiple factors at once? So, for example, not only how cheerful someone is, but how cheerful, depressed, and sleepy they are. And how can you check the quality of your data? How do you make sure you are really measuring what you want to measure?” Questions keep popping up and Joran expects many more to come. For example, what is a good time interval for measurement? How do short-term and long-term development co-exist and influence each other? The field is still in its infancy and there is still plenty to do,” says Joran. At the moment, Joran is mainly focusing on issues surrounding measurement.

Transfer to Tilburg

After his PhD, Joran started working as an assistant professor at Erasmus University Rotterdam. There, in addition to intensive longitudinal data analyses, Joran did many other forms of statistics and worked a lot with applied researchers. After seven years, he was looking for a larger department, so he would be able to exchange ideas with other statisticians. So, Joran came to Tilburg, where there is a large, and very good statistics department, but he can also still work together closely with applied researchers. Collaboration between researchers is facilitated in Tilburg by the Tilburg Experience Sampling Center (TESC), a network of researchers in experience sampling. When Joran started at Tilburg University, he was given an active role in TESC and became part of the board, alongside Eeske van Roekel who was already director of TESC at that time. Joran says of TESC “Collaboration has always been something I enjoyed, and I think it is fantastic that it is at the core of TESC to bring together researchers with common interests but different backgrounds.”

Spearheads for TESC

Joran wants to focus on visibility and education for TESC in the coming period. “I would love for TESC to get even more visibility, internally and externally. We have so many good researchers and in-house expertise. It’s a shame if that’s not used to its full potential. Statistical consultation is fairly well known at the university, but we have many researchers with substantive expertise on how to design studies. They know which practical problems you can run into. It would be great if these researchers are found, they have great projects and collaborations as a result, and if new researchers can use this expertise.” Education is also on Joran’s spearhead list. “What are the needs of PhDs and other researchers, and how can we develop even more gatherings and courses around that? How can we get researchers started with intensive longitudinal data, and supported while working on them, as soon as possible? ”

The future of experience sampling

Experience sampling is gaining popularity and is growing. Why is that? Joran thinks several factors come together. “Mobile phones and watches with sensors for Bluetooth and heart rate make it easier to conduct experience sampling research. The easier it gets the more people will do this type of research. There is also an emerging understanding that it is very useful to employ experience sampling. It gives insight into individuals.” Joran expects the field to continue to develop statistically, but also sees more and more being done with the implementation of the method in practice. “How can we best implement the insights we get from the data into individual therapies and really help people move forward. There is still so much potential there. I am very curious to see how this will develop further,” says Joran enthusiastically.

Good preparation is half the battle

Whether there are any tips for those who want to start with experience sampling? “Yes, definitely,” is Joran’s answer. “Good preparation is half the battle. Especially with experience sampling. Take enough time to set up the study and don’t underestimate it. The execution is 10% of the time and the most important 90% are in the design of the study and the preparation. There are so many things to take into account.  Researchers at TESC can help with this. Above all, involve others because there is a lot of knowledge out there that is not yet written down.” It is also important to realize what you are asking of participants. “If you have to fill out questions five times a day for 3 weeks, that is quite an investment of time. To make sure participants stay engaged, you have to be on top of it, contact them if they miss questions, and teach them how to use the app. ” In short, don’t underestimate it, take your time and ask for help.”

In conclusion

Do you want to know more about Joran’s work? You can check out his publications on Google Scholar or follow him on Twitter.

Did you know that Michael Betancourt has been a major inspiration to Joran, because of his refreshing take on statistics? You can read articles by Michael Betancourt here.

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