Bar Graphs & Baselines: Student Perceptions of Distortions in Real World Graphs

It is important for every educated member of our society to be able to read, comprehend, and interpret graphs. To that end, the National Council of Teachers of Mathematics (NCTM) and the Common Core State Standards have endorsed a kindergarten through eighth-grade mathematics curriculum that is rich in data analysis and graphical literacy skills. These skills are important, as graphs in the public sphere may include certain features that can cause misperceptions of the data. Such features may be intentional or unintentional and can include non-zero baselines, representing data with extra dimensions, stretching and shrinking graphics, not displaying outliers, and more. It is unclear whether the recommended mathematics curriculum prepares students to accurately comprehend these kinds of graphs. This study investigates how effectively the kindergarten through eighth-grade public mathematics curriculum prepares students to read graphs that contain distortions. It focuses on student perceptions and interpretation of data presented in bar graphs. A survey instrument was created to measure student perceptions that included comprehension questions referring to bar graphs with zero baselines and others with non-zero baselines. The instrument was used to assess 181 ninth-grade students in a school in a New England suburb. The results from this survey suggest that many students are susceptible to graphical misperceptions while reading a graph with a non-zero baseline. It suggests that while the current curriculum may include strategies to solve mathematically rigorous graph comprehension problems, it may not equip students with the ability to make simple qualitative conclusions about real world graphs. It is the hope of the researcher that this study may inform future curricula on a local and state level