Methods
Sample Characteristics
The study was conducted at a German university outpatient clinic for
psychotherapy and was approved by the local ethics committee for
psychology. Hypotheses 1-3, sample size, and statistical analyses were
pre-registered on OSF (see https://osf.io/cyzex). Hypothesis 4 was
developed later and, therefore, not pre-registered. Data was collected
from written archive therapy files at the university CBT outpatient
clinic.
To determine the optimal sample size, we conducted an a priori power
analysis using G*Power (Faul, Erdfelder, Lang, & Buchner, 2007). Based
on trauma prevalence in a prior German CBT study (Trautmann et al.,
2019), we assumed a trauma prevalence of 33.3% and calculated sample
size to detect a medium effect size of d = 0.5 between trauma
groups and for both diagnostic groups separately at the standard alpha
error probability of 5% with a power of at least 80%, which yielded an
optimal sample size of N = 340.
Following the results of the power analysis, 340 therapy cases were
included. All therapies took place between 2011 and 2020. Patients were,
on average, 36.97 years old (SD = 13.61) and 64.41% were female.
All patients were diagnosed with either a depression disorder, an
anxiety disorder, or both by their therapist after at least four
diagnostic sessions. On average, patients had 1.54 different psychiatric
diagnoses (SD = 0.65, Min = 1, Max = 4), with
46.47% of all patients having at least one comorbidity. Most frequent
were depression disorders (86.47%), followed by anxiety disorders
(27.94%). Patients diagnosed with PTSD were rare (1.18%). Based on the
criteria described below, 50.88% of all patients were classified as
having experienced at least one traumatic event and belonged to the
trauma group instead of the no-trauma group. Sociodemographic
characteristics by trauma group are displayed in Table 1. For a more
detailed overview, see Supplemental Material, Table 3, Table 4, and
Supplemental Figure 5.
Table 1:
Sociodemographic characteristics of patients at the start of therapy by
trauma group.