Assessing Students' Understanding of Variability in Graphical Representations that Share the Common Attribute of Bars

Everyday encounters with graphical representations include a variety of graphs that superficially appear similar due to their use of bars. This article examines students' conceptions and misconceptions regarding the interpretation of variability in histograms, bar graphs, and value bar charts. A multiple choice assessment with brief written justifications was administered to students in an introductory level college statistics course. Assessment items included comparisons of variability among same-type graphs and questions regarding students' ability to identify key features of the graphs. The study revealed that students struggle to make sense of the underlying structures of the various types of graphs and often disregard graph type as they transfer correct conceptions of variability for one type of graph erroneously to other types of graphs.