title: Effect size calculations for the clinician: methods and comparability.
abstract: OBJECTIVE
  The measurement of clinical change via single-group pre-post effect size has become increasingly common in psychotherapy settings that collect practice-based evidence and engage in feedback-informed treatment. Different methods of calculating effect size for the same sample of clients and the same measure can lead to wide-ranging results, reducing interpretability.
  
  
  METHODS
  Effect sizes from therapists-including those drawn from a large web-based database of practicing clinicians-were calculated using nine different methods.
  
  
  RESULTS
  The resulting effect sizes varied significantly depending on the method employed. Differences between measurement methods routinely exceeded 0.40 for individual therapists.
  
  
  CONCLUSIONS
  Three methods for calculating effect sizes are recommended for moderating these differences, including two equations that show promise as valid and practical methods for use by clinicians in professional practice.
authors.affiliation: a Colorado Center for Clinical Excellence , Denver , CO , USA.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Seidel
authors.forename: Scott D
authors.initials: SD
authors.lastname: Miller
authors.forename: Daryl L
authors.initials: DL
authors.lastname: Chow
mesh_terms: D000328:Adult; D003627:Data Interpretation, Statistical; D006801:Humans; D017063:Outcome Assessment, Health Care / Q000379:methods* / Q000706:statistics & numerical data; D018579:Patient Selection; D011613:Psychotherapy / Q000592:standards* / Q000706:statistics & numerical data; D012107:Research Design / Q000592:standards* / Q000706:statistics & numerical data
keywords: clinical change; effect size; effectiveness; outcome measurement; psychotherapy outcomes