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Latent change score models (LCSMs) are used across disciplines in behavioural sciences to study how constructs change over time. LCSMs can be used to estimate the trajectory of one construct (univariate) and allow the investigation of how changes between two constructs (bivariate) are associated with each other over time. This paper introduces the R package lcsm, a tool that aims to help users understand, analyse, and visualise different latent change score models. The lcsm package provides functions to generate model syntax for basic univariate and bivariate latent change score models with different model specifications. It is also possible to visualise different model specifications in simplified path diagrams. An interactive application illustrates the main functions of the package and demonstrates how the model syntax and path diagrams change based on different model specifications. This R package aims to increase the transparency of reporting analyses and to provide an additional resource to learn latent change score modelling.

Although trauma-focused cognitive therapy for PTSD is effective and recommended in international treatment guidelines as a first-line intervention for PTSD, the psychological processes through which this treatment drives clinical improvement have rarely been investigated. The aim of this thesis is to improve our understanding of how cognitive therapy for PTSD works by testing predictions made by Ehlers and Clark’s (2000) cognitive model of PTSD in two large datasets of patients receiving cognitive therapy in routine care (N1 = 330; N2 = 343). To increase the transparency and reproducibility of my work, I developed research software tools that help implement the methods used in this thesis in a transparent and reproducible way. I used bivariate latent change score models to test whether changes in the PTSD symptoms are preceded by changes in theory-derived cognitive processes and coping strategies during treatment. The results show that changes in PTSD symptoms were preceded by changes in negative appraisals, flashback quality of unwanted memories, and unhelpful responses to intrusions, but not vice versa. The relationship between changes in trauma memory disorganisation and changes in PTSD symptoms was bidirectional. To investigate sudden symptom improvements during cognitive therapy for PTSD I developed the R package suddengains. First, I examined how cognitive factors change before, during, and after sudden gains in PTSD symptom severity. The results indicate that sudden gains were accompanied, and to a smaller degree preceded, by improvements in negative appraisals and flashback quality of unwanted memories. A second study extended these results by exploring improvement in individual PTSD, depression, and anxiety symptoms during sudden gains in total PTSD symptoms. The results suggest that patients experience different patterns of sudden symptom improvements, while showing similar overall treatment outcomes. The studies presented in this thesis contribute further evidence supporting predictions about maintenance factors and clinical recovery during treatment by Ehlers and Clark’s (2000) cognitive model of PTSD. This thesis also contributed to clinical research methodology by developing research software that facilitates reproducible analyses as well as a collaborative evaluation and further development of methods evaluating processes of change in psychological therapies. Overall, this thesis supports interventions targeting the identification and modification of cognitive and behavioural processes in PTSD.

Objective: Although most studies investigating sudden gains in treatments for posttraumatic stress disorder (PTSD) report a positive association between sudden gains and outcomes at the end of treatment, less is known about sudden gains in routine clinical care and the processes involved in their occurrence. This study investigated changes in cognitive factors (negative appraisals, trauma memory characteristics) before, during, and after sudden gains in PTSD symptom severity. Method: Two samples (N1 = 248, N2 = 234) of patients who received trauma-focused cognitive therapy for PTSD in routine clinical care were analyzed. Mahalanobis distance matching, including the propensity score, was used to compare patients with sudden gains and similar patients without sudden gains. Estimates from both samples were meta-analyzed to obtain pooled effects. Results: Patients with sudden gains (n1 = 76, n2 = 87) reported better treatment outcomes in PTSD symptom severity, depression, and anxiety at the end of therapy and follow-up than those without sudden gains. No baseline predictors of sudden gains could be reliably identified. During sudden gains, those with sudden gains had greater changes in both cognitive factors than matched patients. Meta-analyses of the two samples showed that negative appraisals had already decreased in the session prior to sudden gains compared with matched patients. Conclusions: The pooled estimates suggest that changes in negative trauma-related appraisals precede sudden gains in PTSD symptoms. The results suggest that interventions that promote change in appraisals may also facilitate sudden gains in therapy., What is the public health significance of this article? This study highlights that a substantial subgroup of patients with PTSD showed concurrent large improvements in PTSD, appraisals, and memory features from one treatment session to the next. Sudden gains were also preceded by greater changes in appraisals than sessions that did not include sudden gains. This supports interventions that target the identification and modification of negative appraisals in PTSD, which, if successful, can result in sudden symptom improvements that are associated with better treatment outcomes.

Background: Adolescent cancer survivors are a particularly vulnerable group of young patients. Compared with healthy peers, adolescent survivors face more psychosocial difficulties and are at increased risk of developing psychiatric disorders. Aims: We aimed to establish prevalence rates and predictors of psychiatric disorders in young cancer survivors and discuss areas for targeted interventions. Method: We systematically reviewed four major online databases: Embase, PsychINFO, Scopus, and Medline for quantitative studies evaluating mental health in adolescent cancer survivors. We used a narrative synthesis approach. Results: Nineteen studies met our inclusion criteria. Across the sample, up to 34% met criteria for post‐traumatic stress disorder (PTSD), 13% for clinical depression, and 8% for anxiety. Maladaptive coping, illness relapse, higher number of late effects, brain tumor diagnosis, and poor family functioning and parental distress were associated with higher psychological distress. Conclusions: A significant subset of adolescent survivors reports PTSD, anxiety, and depression symptoms. Individuals who present with more vulnerabilities and higher risk indices should be routinely assessed in order to reduce the psychological, social, and economic burden associated with poor mental health in this population. Early prevention strategies should target maladaptive coping mechanisms and promote healthy peer relationships and family functioning.