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data files, results, and code used to conduct the analyses in this manuscript as well as a number of additional analyses referenced in footnotes in the manuscript. A web application (https://emoriebeck.shinyapps.io/pairs_graphicalvar/) contains visualizations of the more than 700 networks constructed in the analyses.

Preregistration clarifies the distinction between planned and unplanned research by reducing unnoticed flexibility. This improves credibility of findings and calibration of uncertainty. However, making decisions before conducting analyses requires practice. During report writing, respecting both what was planned and what actually happened requires good judgment and humility in making claims.

Since its beginnings, personality psychology has focused on both nomothetic and idiographic questions, but nomothetic approaches have captured the majority of attention in the past century. In this article, we demonstrate how recent measurement and modeling techniques provide an avenue for testing idiographic propositions about the dynamic features of a personality system. Findings indicate that people have unique structures of personality and that these structures are sensitive to situations people encounter. At the same time, these unique, mutable systems show longitudinal consistency for some but not all people.

Objectives Life experiences are thought to prompt changes in personality. However, existing studies find few replicable mean-level changes in personality following life events. The focus on mean-level change may obscure other types of personality change that are not routinely studied in the context of life events. These are: variability in response, structural, and ipsative change. Method The current proposal examines whether major life events (e.g., divorce, job loss) impact these three understudied types of personality trait change using three waves of Big Five trait data in a large-scale, representative longitudinal study (GSOEP, N = 16,368). Structural equation models compare those who had an event to their prior self and a control group that did not experience the event. Results Life events were found to have mostly null or small effects on variability in response, structural, and ipsative change. Across two types of tests for variability in response few replications occurred. The only consistent effect across three types of change were for mental health events, which served to increase variance in all Big Five traits and increase consistency in ipsative profiles.

From its emergence at the beginning of the 20th century, personality scientists pursued two goals – a nomothetic approach that investigated the structure of individual differences between people in a population and an idiographic approach that explored variation within a person relative to him or herself. In this chapter, we first track the how the history of these two perspectives impacted the study of within-person variability. Next, we review findings and unanswered contemporary questions regarding within-person variability. Finally, we conclude by providing questions for future research, some of which were proposed by early personality theorists but progressed slowly due to a lack of adequate methods. We outline cutting-edge statistical models and idiographic techniques to move the study of within-person variability – and personality science – forward.

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Theorists and clinicians have long noted the need for idiographic (i.e., individual-level) designs within clinical psychology. Results from idiographic work may provide a possible resolution of the therapist's dilemma -the problem of treating an individual using information gathered via group-level research. Due to advances in data collection and time series methodology, there has been increasing interest in using idiographic designs to answer clinical questions. Although time series methods have been well-studied outside the field of clinical psychology, there is limited direction on how clinicians can use such models to inform their clinical practice. In this primer, we collate decades of published and word-of-mouth information on idiographic designs, measurement, and modeling. We aim to provide an initial guide on the theoretical and practical considerations that we urge interested clinicians to consider before conducting idiographic work of their own.