155 General Discussion 7 Chapter 5 applied idiographic network analysis to model each individual’s 60-day personality-related change process. Results show high betweenperson heterogeneity in network structures, even within subgroups that share the same personality profile. Repeatedly estimating each individual's network in a sliding 30-day window revealed non-stationarity in each person’s estimate. This was unsurprising, given that complex systems theoretical accounts of personality suggest processes likely to be nonstationary. However, it does invalidate aggregated network estimates, which is problematic because capturing individuals’ stable personality networks is required to subsequently reliably assess individual differences. To remedy these problems, it is imperative to 1) build theory on the to-be-modeled timeframe, timescale(s), and idiographic network components and 2) include, collect, and analyze time-specific contextual information. Chapter 6 then described a case study of one woman’s self-reported challenging behaviors with contextual information during the course of 560 days. Qualitative analyses of caretaker records resulted in a holistic summary of her life, which added time-specific contextual information to the quantitative diary data. Staff narrowed this extensive qualitative summary down to 11 staff-hypothesized risk-/protective factors. Results showed that challenging behavior was more likely the day after a coercive measure, and less likely the day after therapy. Staff-hypothesized causes (a.o. reliving trauma, hallucinating, pain, negative affect, family tensions) were not associated with challenging behavior, underscoring that it is a complex phenomenon that is not governed by simple if-then relations. The participant’s timeline had different stable phases that alternated between different attractor states: combinations of high, average, and low challenging behavior. Most phase transitions were preceded by instability and/or exceptional events (e.g., the Covid lockdown). Discussion of findings This dissertation assessed how and why the behaviors of young people with a mild intellectual disability change over time. In Chapter 1 I introduced the two routes to studying change, the nomothetic and the idiographic approach, using the metaphor of looking at people through a microscope with different lenses. Chapters 2 and 3 started out with relatively wide-angle lenses, applying a nomothetic method that looks broadly at group-level behavioral change. We concluded that Take it Personal! was one reason why substance use changed on average. Chapter 4 introduced a method that enables both nomothetic and idiographic studies of
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