The symbolization styles they examined were size-based circles and bars, shadings (value), pure (circles, bars, and shadings), combined (shadings and distortion), circles, and bars. To measure the effectiveness of these symbolization styles, the researchers examined decision accuracy, decision confidence, decision efficiency, and perceived ease of task. Below is a chart of their findings.
The researchers found that using circles was the most effective visualization methods for decision makers. Using all four measures of effectiveness, circle symbolization was the best performing one. Other results showed the combined shadings and distortion ranked second in decision accuracy, but ranked lowest in decision confidence. Value shadings ranked lowest in decision efficiency while shadings and bars ranked lowest in perceived ease of task.
This study has direct implications to intelligence analysts. This study found that circle symbolization of quantitative information is the most effective symbolization tool for decision makers. As intelligence analysts, it is our job to continue to improve communication between ourselves and our decision makers. The results of this study can help us do that. Since GIS data can be used by all types of intelligence (national security, law enforcement, and competitive), this study can be applied across all fields as well.
The only criticism I have is that circles as a form of quantitative symbolization may not be applicable to all types of scenarios or quantitative data. Though at this moment I cannot think of any, there might be a situation where circles are not the best form of visualization.
Source: Ozimec, A., Natter, M., & Reutterer, T. (2010). Geographical Information Systems–Based Marketing Decisions:Effects of Alternative Visualizations on Decision Quality. Journal of Marketing, 74 (6), 94-110. Retrieved from http://ehis.ebscohost.com/eds/pdfviewer/pdfviewer?sid=8fe30abf-7ab8-4068-be2c-26bac62fd9d7%40sessionmgr4&vid=2&hid=4#