Effect Sizes in Single Case Research: How Large is Large?

Abstract

This study examined the problem of interpreting effect sizes in single case research. Nine single case analytic techniques were applied to a convenience sample of 77 published interrupted time series (AB) datasets, and the results were compared by technique across the datasets. Reanalysis of the published data helped answer questions about the nine analytic techniques: their effect sizes, autocorrelation, statistical power, and intercorrelations. The study's findings were that few effect sizes matched Cohen's (1988) guidelines, and that effect sizes varied greatly by analytic technique. Four techniques showed adequate power for typical published data series. Autocorrelation was a sizeable problem in most analyses. In general, individual techniques performed so differently that users need technique-specific information to guide both selection of an analytic technique and interpretation of its results.

Additional information

Notes on contributors

Richard I. Parker

Richard Parker received his doctorate in special education at the University of Oregon in 1990 and is an Associate Professor in the Special and Bilingual Education program at Texas A&M University. His professional interests include evaluation research, alternative assessment, and international education.

Daniel F. Brossart

Dan Brossart received his doctorate in counseling psychology from the University of Missouri-Columbia in 1996. He is an Associate Professor in the Counseling Psychology program at Texas A&M University. His research interests include intervention research and psychotherapy processes.

Kimberly J. Vannest

Kimberly Vannest received her doctorate in 2000 from the University of Baton Rouge in Curriculum and Instruction/Special Education. She is an Assistant Professor in the Special and Bilingual Education program at Texas A&M University. Her research interests include classroom interactions, effective instruction, and emotional/behavioral disabilities.

James R. Long

James Long received his doctorate in counseling psychology in 2003 from Texas A&M University and is currently completing a Geropsychology Post-Doctoral Fellowship at the VA Palo Alto Health Care System.

Roman Garcia De-Alba

Roman De-Alba is currently completing the internship requirements for a doctorate in school psychology from Texas A&M University in the Cypress-Fairbanks ISD, Texas.

Frank G. Baugh

Frank Baugh received his doctorate in counseling psychology in 2004 from Texas A&M University and is currently beginning a postdoctoral residency in organization consultation and development through the National Center for Organization Development in Cincinnati, Ohio.

Jeremy R. Sullivan

Jeremy Sullivan received his doctorate in school psychology in 2003 from Texas A&M University and is currently a school psychologist for Cypress-Fairbanks ISD, Texas.