Unpacking the therapist effect: Impact of treatment length differs for high- and low-performing therapists.
Differences between therapists in their average outcomes (i.e., therapist effects) have become a topic of increasing interest in psychotherapy research in the past decade. Relatively little work, however, has moved beyond identifying the presence of significant between-therapist variability in patient outcomes. The current study sought to examine the ways in which therapist effects emerge over the course of time in psychotherapy.



We used a large psychotherapy data set (n = 5828 patients seen by n = 158 therapists for 50,048 sessions of psychotherapy) and examined whether outcomes diverge for high-performing (HP) and low-performing (LP) therapists as treatment duration increases.



Therapists accounted for a small but significant proportion of variance in patient outcomes that was not explained by differences between therapists' caseload characteristics. The discrepancy in outcomes between HP and LP therapists increased as treatment duration increased (interaction coefficient = 0.071, p < .001). In addition, patients' trajectories of change were a function of their therapist's average outcome as well as the patient's duration of treatment (interaction coefficient = 0.060, p = .040).



Indeed, patterns of change previously described ignoring between-therapist differences (e.g., dose-effect, good-enough level model) may vary systematically when disaggregated by therapist effect.
a Department of Counseling Psychology , University of Wisconsin-Madison , Madison , WI , USA.
Simon B
SB
Goldberg
a Department of Counseling Psychology , University of Wisconsin-Madison , Madison , WI , USA.
William T
WT
Hoyt
b Department of Psychology , University of Oslo , Oslo , Norway.
Helene A
HA
Nissen-Lie
c Counseling and Psychological Services , Brigham Young University , Provo , UT , USA.
Stevan Lars
SL
Nielsen
a Department of Counseling Psychology , University of Wisconsin-Madison , Madison , WI , USA.|d Modum Bad Psychiatric Center , Vikersund , Norway.
Bruce E
BE
Wampold
D000328:Adult; D006282:Health Personnel / Q000706:statistics & numerical data*; D006801:Humans; D001523:Mental Disorders / Q000628:therapy*; D015233:Models, Statistical; D055361:Multilevel Analysis; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data*; D011613:Psychotherapy / Q000706:statistics & numerical data*; D013997:Time Factors; D000066477:Work Performance / Q000706:statistics & numerical data*
dose-effect; dose–response; good-enough level; multilevel modeling; therapist effects; trajectories of change