As most other empirical investigations, this dissertation shows certain strengths but al-so al-some weaknesses, which both have to be taken into account when addressing the clinical significance of the findings. Most prominent among the weaknesses is the retrospective as-sessment of the therapeutic alliance, which has been discussed in great detail in the discussion sections of the corresponding empirical studies. The problematic aspect about the retrospec-tive alliance measurement is that one assumption, namely that the two therapist variables un-der investigations would influence the therapists’ ability to form positive alliances, which would thereupon result in positive or negative outcomes, cannot be tested directly. The pre-sent design only allows a correlative identification of empirical associations of the therapist variables with alliance and outcome. Alliance measurements during early phases of therapy would be necessary to test the mediation hypothesis formulated above.
A second weakness pertains to the sample size of therapists that could be included.
From the first to the fourth study, the therapist sample dropped from 50 to twelve. A sample size of 50 on the highest level is adequate for multilevel analyses, a sample size of 31 thera-pists in the second and third study is just above the required minimum of 30 units (Hox, 2002). However, the 12 therapists that could be included in the fourth study are not enough in order to come up with conclusions that can be generalized to other inpatient therapist samples.
Therefore, the findings from the fourth study should be treated with caution and might rather serve as an explorative pilot study. On the other hand, the methodological approach with a 3-parameter regression model for the modelling of alliance development proved of value, and secondly, the findings can generate new hypotheses about the influence of therapists’ attach-ment preoccupation. However, the results need to be replicated in larger samples.
A third weakness is the selection of therapists included in the four studies. The main theoretical orientation of all participating clinics was psychodynamic and therapists also had a mainly psychoanalytic/psychodynamic background. When investing common factors, one should assume that their influence may be similar across different theoretical orientations;
however this cannot be claimed unless it is tested empirically. It is therefore unknown, wheth-er thwheth-erapist attachment has the same effect in psychodynamic as in cognitive-behavioral or other treatments, especially when the research on attachment influences reaches a stages that allows the deduction of specific, evidence-based guidelines for therapeutic practice.
Besides these weaknesses, the studies included in this dissertation show some major advantages. The first one ironically pertains to the sample size (again): Even though the num-ber of therapists in the fourth study seems problematic, the numnum-ber of therapists included in study one to three is a positive exception in the literature on therapist effects, where often small-scale studies with a significantly lower numbers of therapists are published (Beutler et al., 2004; Soldz, 2006). In addition, each therapist included in this study treated a relatively large number of patients (minimum of ten patients for studies one to three, overall patient sample exceeds 1,000). This increases the likelihood that more reliable estimations of thera-pists’ actual ability to form alliances or reach positive outcomes are achieved and allows the investigation of interaction effects between patients and therapists.
A second strength of the present work is the use of the AAI in studies three and four.
Interview-based measures of attachment are more expensive and time-consuming compared to self-reports, but in exchange they allow for classifications with greater external validity.
Especially with regard to general adult caregiving behavior, the classical findings from which the hypotheses had been deduced were all obtained from studies using expert ratings for stan-dardized assessment procedures, mainly the AAI. A basic principle in experimental science is that variations of several factors at a time is problematic for the interpretation of new effects, as it is not clear which manipulation caused the new effect.
A third strength of the study is the relatively sophisticated multilevel approach that was used for the statistical analyses of the nested data, including a 3-level model in the fourth study. Multilevel models are becoming increasingly popular in psychotherapy research, as oftentimes repeated measurements are nested within patients, or patients are nested within therapists (as was the case the present study) or therapists are themselves nested in organiza-tions, cities, theoretical approaches and numerous other variables. The multilevel models al-lowed the computation of interaction effects between variables on the patient level with thera-pist variables without having to aggregate or disaggregate data.
Another major strength of our research is that it may serve as a positive reference and as an icebreaker for future studies on therapist factors in psychodynamically oriented settings.
The participating therapists were sceptical in the beginning, presumingly because a scientific, quantifiable evaluation of therapist factors is not very common in the psychodynamic com-munity (apart from clinical reflections in personal therapy and supervision, of course). Espe-cially the possible evidence-based identification of “good” and “bad” clinicians caused fear among therapists. However, the strict level of anonymity that was guaranteed as well as a
de-tailed theoretical introduction about the clinical relevance of the work resulted in high accep-tance levels. From 21 therapists that were approached for the attachment study in one clinic, 19 participated and all therapists from the second clinic participated in the attachment study.
Furthermore, during the ongoing study, new therapists joined the clinic, heard about the study and asked to also be included. Therapists reported that they enjoyed the attachment interview and all therapists wanted to know their attachment classification as well as their outcome ranking in relation to other therapists after the study was completed.
The four studies that make up this dissertation comprise the first systematic and em-pirical investigation of therapist factors in inpatient psychotherapy. The investigation of thera-pist factors seems of high clinical significance, as they represent a possible starting point for treatment optimizations. The large share of patient influence on outcome variance has to be taken as a prerequisite in psychotherapy, as a low motivation to change, high symptom load, and numerous other patient variables related to negative outcomes are part of the problem that should be approached by the treatment. However, this is different for therapist variables: if the understanding about possible negative influences of certain therapist variables (as well as knowledge about the positive influence of others) increases, this knowledge might change therapeutic manuals, general therapist training, supervision and therapists’ personal reflec-tions in therapy.