To investigate the size of therapist effects using multilevel modeling (MLM), to compare
the outcomes of therapists identified as above and below average, and to consider
how key variables--in particular patient severity and risk and therapist caseload--contribute
to therapist variability and outcomes.
We used a large practice-based data set comprising patients referred to the U.K.'s
National Health Service primary care counseling and psychological therapy services
between 2000 and 2008. Patients were included if they had received ≥2 sessions of
1-to-1 therapy (including an assessment), had a planned ending to treatment, and completed
the Clinical Outcomes in Routine Evaluation-Outcome Measure (CORE-OM; Barkham et al.,
2001; Barkham, Mellor-Clark, Connell, & Cahill, 2006; Evans et al., 2002) at pre-
and post-treatment. The study sample comprised 119 therapists and 10,786 patients,
whose mean age was 42.1 years (71.5% were female). MLM, including Markov chain Monte
Carlo procedures, was used to derive estimates to produce therapist effects and to
analyze therapist variability.
The model yielded a therapist effect of 6.6% for average patient severity, but it
ranged from 1% to 10% as patient non-risk scores increased. Recovery rates for individual
therapists ranged from 23.5% to 95.6%, and greater patient severity and greater levels
of aggregated patient risk in a therapist's caseload were associated with poorer outcomes.
The size of therapist effect was similar to those found elsewhere, but the effect
was greater for more severe patients. Differences in patient outcomes between those
therapists identified as above or below average were large, and greater therapist
risk caseload, rather than non-risk caseload, was associated with poorer patient outcomes.
© 2012 American Psychological Association