Evaluating the impact of clutter in Euler diagrams

Euler diagrams, used to visualize data and as a basis for visual languages, are an effective representation of information, but they can become cluttered. Previous research established a measure of Euler diagram clutter, empirically shown to correspond with how people perceive clutter. However, the impact of clutter on user understanding is unknown. An empirical study was executed with three levels of diagram clutter. We found a significant effect: increased diagram clutter leads to significantly worse performance, measured by time and error rates. In addition, we found a significant effect of zone (a region in the diagram) clutter on time and error rates. Surprisingly, the zones with a middle level of clutter had the highest error rate compared to the zones with lowest and the highest clutter. Also, the questions whose answers were placed in zones with medium clutter had the highest mean time taken to answer questions. In conclusion, both diagram clutter and zone clutter impact the interpretation of Euler diagrams. Consequently, future work will establish whether a single, but cluttered, Euler diagram is a more effective representation of information than multiple, but less cluttered, Euler diagrams.