Calculating Effect Size

Calculating Effect Size

"Effect size is a statistical concept that measures the strength of the relationship between two variables on a numeric scale” (Statistics Solutions, 2013, para. 1). In layman's terms, effect size helps researchers determine the difference between two variables. For instance, if you have data about whether high school students learn better in the morning or the afternoon and your experiment included 42 students, your average score of the morning group versus the afternoon group would distinguish a difference in score.

However, ‘How big is the difference?’ is really the defining question. In essence, determining “effect size will resolve the problem. In single-case design, Cohen’s d is often used to calculate the difference between two means in standard deviation units.

To Prepare

Review the “Sample Multiple Baseline Data” document found in the Learning Resources.
Follow the instructions in the “Sample Multiple Baseline Data” document in order to manually calculate the effect size of each data set.
Review the media regarding how to calculate effect size.
To check your work, use the effect size calculator found in the Becker (2000) Learning Resource, to calculate the effect size of each dataset. This will give you a clear indication if your calculations are correct.

Resources

• Kazdin, A. E. (2021). Single-case research designs: Methods for clinical and applied settings (3rd ed.). Oxford University Press.
  • Chapter 4, “Methods of Assessment” (pp. 95–127)
    (previously read in Week 3)
  • Appendix, “Guidelines for Conducting, Reporting, and Evaluating Single-Case Research” (pp. 495–518)
• Solomon, B. G. (2014). Violations of assumptions in school-based single-case data: Implications for the selection and interpretation of effect sizes. Links to an external site.Behavior Modification, 38 , 477-496. doi: 10.1177/0145445513510931
• Document: Case Study Performance Tasks Download Case Study Performance Tasks(Word document)
• Document: Sample Multiple Baseline Data Download Sample Multiple Baseline Data(PDF document)
• Document: Example of Visual Analysis Download Example of Visual Analysis(PDF document)