Only for ergodic processes will inferences based on group-level data generalize to individual experience or behavior. Because human social and psychological processes typically have an individually variable and time-varying nature, they are unlikely to be ergodic. In this paper, six studies with a repeated-measure design were used for symmetric comparisons of interindividual and intraindividual variation. Our results delineate the potential scope and impact of nonergodic data in human subjects research. Analyses across six samples (with 87-94 participants and an equal number of assessments per participant) showed some degree of agreement in central tendency estimates (mean) between groups and individuals across constructs and data collection paradigms. However, the variance around the expected value was two to four times larger within individuals than within groups. This suggests that literatures in social and medical sciences may overestimate the accuracy of aggregated statistical estimates. This observation could have serious consequences for how we understand the consistency between group and individual correlations, and the generalizability of conclusions between domains. Researchers should explicitly test for equivalence of processes at the individual and group level across the social and medical sciences.

Individual variation is increasingly recognized as important to psychopathology research. Concurrently, new methods of analysis based on network models are bringing new perspectives on mental (dys)function. This current work analyzed idiographic multivariate time series data using a novel network methodology that incorporates contemporaneous and lagged associations in mood and anxiety symptomatology. Data were taken from 40 individuals with generalized anxiety disorder (GAD), major depressive disorder (MDD), or comorbid GAD and MDD, who answered questions about 21 descriptors of mood and anxiety symptomatology 4 times a day over a period of approximately 30 days. The model provided an excellent fit to the intraindividual symptom dynamics of all 40 individuals. The most central symptoms in contemporaneous systems were those related to positive and negative mood. The temporal networks highlighted the importance of anger to symptomatology, while also finding that depressed mood and worry-the principal diagnostic criteria for GAD and MDD-were the least influential nodes across the sample. The method's potential for analysis of individual symptom patterns is demonstrated by 3 exemplar participants. Idiographic network-based analysis may fundamentally alter the way psychopathology is assessed, classified, and treated, allowing researchers and clinicians to better understand individual symptom dynamics. (PsycINFO Database Record

The proposed approach has the potential to inform the construction and implementation of personalized treatments by delineating the idiosyncratic structure of psychopathology on a person-by-person basis.

Objective The goal of the current study was to examine mechanisms of change in Prolonged Exposure (PE) therapy for post-traumatic stress disorder (PTSD). Emotional Processing Theory of PTSD proposes that disconfirmation of erroneous cognitions associated with PTSD is a central mechanism in PTSD symptom reduction; but to date, the causal relationship between change in pathological cognitions and change in PTSD severity has not been established. Method Female sexual or nonsexual assault survivors (N = 64) with a primary diagnosis of PTSD received 10 weekly sessions of PE. Self-reported PTSD symptoms, depression symptoms, and PTSD-related cognitions were assessed at pre-treatment, each of the 10 PE treatment sessions, and post-treatment. Results Lagged mixed-effect regression models indicated that session-to-session reductions in PTSD-related cognitions drove successive reductions in PTSD symptoms. By contrast, the reverse effect of PTSD symptom change on change in cognitions was smaller and did not reach statistical significance. Similarly, reductions in PTSD-related cognitions drove successive reductions in depression symptoms whereas the reverse effect of depression symptoms on subsequent cognition change was smaller and not significant. Notably, the relationships between changes in cognitions and PTSD symptoms were stronger than the relationships between changes in cognitions and depression symptoms. Conclusions To our knowledge, this is the first study to establish change in PTSD-related cognitions as a central mechanism of PE treatment. These findings are consistent with Emotional Processing Theory and have important clinical implications for the effective implementation of PE.

Clinicians have long recognized the importance of tailoring psychotherapy interventions to the needs and characteristics of the individual patient. However, traditional approaches to clinical assessment, service delivery, and intervention research have not been conducive to such personalization. Contrary to traditional nomothetic approaches, idiographic assessment and modeling of intraindividual dynamic processes holds tremendous promise for tailoring the implementation of psychotherapy to the individual patient. In this article, we (a) present an argument for assessing person-specific dynamics, (b) provide a detailed description of a method that harnesses person-specific dynamic assessment and modeling for use in routine psychotherapy,