title: The relationship between session frequency and psychotherapy outcome in a naturalistic setting.
abstract: OBJECTIVE
  The dose-response relationship in psychotherapy has been examined extensively, but few studies have included session frequency as a component of psychotherapy "dose." Studies that have examined session frequency have indicated that it may affect both the speed and the amount of recovery. No studies were found examining the clinical significance of this construct in a naturalistic setting, which is the aim of the current study.
  
  
  METHODS
  Using an archival database of session-by-session Outcome Questionnaire 45 (OQ-45) measures over 17 years, change trajectories of 21,488 university counseling center clients (54.9% female, 85.0% White, mean age = 22.5) were examined using multilevel modeling, including session frequency at the occasion level. Of these clients, subgroups that attended therapy approximately weekly or fortnightly were compared to each other for differences in speed of recovery (using multilevel Cox regression) and clinically significant change (using multilevel logistic regression).
  
  
  RESULTS
  Results indicated that more frequent therapy was associated with steeper recovery curves (Cohen's f2 = 0.07; an effect size between small and medium). When comparing weekly and fortnightly groups, clinically significant gains were achieved faster for those attending weekly sessions; however, few significant differences were found between groups in total amount of change in therapy.
  
  
  CONCLUSIONS
  Findings replicated previous session frequency literature and supported a clinically significant effect, where higher session frequency resulted in faster recovery. Session frequency appears to be an impactful component in delivering more efficient psychotherapy, and it is important to consider in individual treatment planning, institutional policy, and future research.
authors.affiliation: Department of Psychology.
authors.forename: David M
authors.initials: DM
authors.lastname: Erekson
authors.affiliation: Department of Psychology.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Lambert
authors.affiliation: Department of Statistics.
authors.forename: Dennis L
authors.initials: DL
authors.lastname: Eggett
mesh_terms: D000328:Adult; D003376:Counseling / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D008605:Mental Health Services / Q000706:statistics & numerical data*; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data*; D011613:Psychotherapy / Q000706:statistics & numerical data*; D013333:Student Health Services / Q000706:statistics & numerical data*; D011795:Surveys and Questionnaires; D055815:Young Adult