| Summary: | <p>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 (N<sub>1</sub> = 330; N<sub>2</sub> = 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.</p>
<p>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.</p>
<p>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.</p>
<p>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.</p>
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