Assessing understanding of the concept of interaction in analysis of variance

Students have difficulty understanding the concept of interaction in analysis of variance, implications of the presence of a significant interaction for interpretation of main effects, and appropriate follow-up procedures. While grasping computational procedures and how to get software to generate the appropriate terms, interpretation and communication of results poses a challenge. In this paper exercises for teaching interpretation of interaction are presented. The context was an anova course designed for doctoral students in a college of education. These students are typically interested in substantive research areas such as counseling or educational administration, so the course is applied in nature. The approach taken to teaching interaction was scaffolding or layering of skills. Students first listened to explanations and examples of what interaction is and answered multiple choice questions oriented to comprehension and application outside of class. They then worked in small groups in class to calculate interaction terms both by hand and using statistical software. Next students wrote both technical summaries of results suitable for submission to a journal and one-paragraph “press releases,” both of which were critiqued by the course instructor and graduate teaching assistant. These exercises were standard across students and were highly structured. Students then received different data sets and were asked to repeat the analysis, technical, and brief write-up of results for the new data as a homework exercise. The “press releases” were the basis of 5-minute in-class presentations done to encourage verbal communication of results. After the presentation, classmates were given a 3-item quiz about their understanding of the results just presented. The quiz responses were used as feedback to the presenter about the effectiveness of their communication. Successes and failures of this approach are discussed as are thoughts about future directions in teaching about interaction.