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Several proposals have been made to grade the available evidence of both medical and psychotherapeutic treatments (Canadian Task Force on the Periodic Health Examination, 1979; Chambless & Hollon, 1998; Clarke & Oxman, 2003; Cook, Guyatt, Laupacis, Sacket, & Goldberg, 1995; Nathan & Gorman, 2002). Apart from other differences, all available proposals regard RCTs (efficacy studies) as the ‘gold standard’ for the demonstration that a treatment is effective. According to this view, only RCTs can provide level I evidence, which is the highest level of evidence. RCTs are conducted under controlled experimental conditions, allowing one to control for variables systematically influencing the outcome apart from the treatment. The defining feature of an RCT is the random assignment of subjects to the different conditions of treatment (Shadish, Cook, & Campbell, 2002). Randomization is regarded as indispensable in order to ensure that a priori existing differences between subjects are equally distributed. The goal of randomization is to attribute the observed effects exclusively to the applied therapy. Thus, randomization is used to ensure the internal validity of a study (Shadish et al., 2002). Gabbard, Gunderson, and Fonagy (2002) discuss different types of RCTs that provide different levels of evidence. The most stringent test of efficacy is achieved by comparison with rival treatments, thus controlling for specific and unspecific therapeutic factors (Chambless & Hollon, 1998, p. 8). Furthermore, such comparisons provide explicit information regarding the relative benefits of competing treatments. Treatments that are found to be superior to rival treatments are more highly valued. As RCTs are carried out under controlled experimental conditions, their internal validity is usually high. However, for this very reason, their external validity may be limited, in that their results may not be fully representative of clinical practice. In contrast to RCTs, naturalistic studies (observational or effectiveness studies) are conducted under the conditions of clinical practice. Thus, their results are usually more representative for clinical practice with regard to patients, therapists, and treatments (external validity). RCTs and observational studies address different questions of research, i.e., efficacy under controlled experimental conditions versus effectiveness under the conditions of clinical practice (Leichsenring, 2004). For this reason, RCTs are not ‘bad’ and observational studies are not ‘good’ or vice versa. Their relationship is complementary rather than one of rival (Leichsenring, 2004). =&.4$'2! O0:$*$($)*!):!/647#)&4*29$7!"#0%214![/O"^! PDT operates on an interpretive-supportive continuum (Gunderson & Gabbard, 1999; Wallerstein, 1989). Interpretive interventions enhance the patient’s insight about repetitive conflicts sustaining his or her problems (Gabbard, 2004; Luborsky, 1984). Supportive interventions aim to strengthen abilities (‘ego-functions’) that are temporarily not accessible to a patient due to acute stress (e.g., traumatic events) or that have not been sufficiently developed (e.g., impulse control in borderline personality disorder; BPD). Thus, supportive interventions maintain or build ego functions (Wallerstein, 1989). Supportive interventions include, for example, fostering a therapeutic alliance, setting goals, or strengthening ego functions such as reality testing or impulse control (Luborsky, 1984). The use of more supportive or more interpretive (insight-enhancing) interventions depends on the patient’s needs. The more severely disturbed a patient is, or the more acute his or her problem is, the more supportive and less interpretive interventions are required and vice versa (Luborsky, 1984; Wallerstein, 1989). Borderline patients, as well as healthy subjects, in an acute crisis or after a traumatic event may need more supportive interventions (e.g., stabilization, providing a safe and supportive environment). Thus, a broad spectrum of psychiatric problems and disorders can be treated with PDT, ranging from milder adjustment disorders or stress reactions to severe personality disorders such as BPD or psychotic conditions.
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