Sara Johansson Fernstad

Sara Johansson Fernstad, Jimmy Johansson

This paper contributes a novel visualization method, Missingness Glyph, for analysis and exploration of missing values in data. Missing values are a common challenge in most data generating domains and may cause a range of analysis issues. Missingness in data may indicate potential problems in data collection and pre-processing, or highlight important data characteristics. While the development and improvement of statistical methods for dealing with missing data is a research area in its own right, mainly focussing on replacing missing values with estimated values, considerably less focus has been put on visualization of missing values. Nonetheless, visualization and explorative analysis has great potential to support understanding of missingness in data, and to enable gaining of novel insights into patterns of missingness in a way that statistical methods are unable to. The Missingness Glyph supports identification of relevant missingness patterns in data, and is evaluated and compared to two other visualization methods in context of the missingness patterns. The results are promising and confirms that the Missingness Glyph in several cases perform better than the alternative visualization methods.

Nicolas S. Holliman, Arzu Coltekin, Sara J. Fernstad et al.

Background: Even though data visualizations (and underlying data) almost always contain uncertainty, it remains complex to communicate and interpret uncertainty representations. Consequently, uncertainty visualizations for non-expert audiences are rare. Objective: our aim is to rigorously define and evaluate the novel use of visual entropy as a measure of shape that allows us to construct an ordered scale of glyphs for use in representing both uncertainty and value in 2D and 3D environments. Method: We use sample entropy as a numerical measure of visual entropy to construct a set of glyphs using R and Blender which vary in their complexity. Results: an exact binomial analysis of a pairwise comparison of the glyphs shows a majority of participants (n = 87) ordered each glyph as predicted by the visual entropy score with large effect size (Cohen's g > 0.25). We also evaluate whether the glyphs effectively represent uncertainty using a signal detection method in a search task. Participants (n = 15) were able to find glyphs representing uncertainty with high sensitivity and low error rates. Conclusion: visual entropy is a successful novel approach to representing ordered data and provides a channel that can allow the uncertainty of a measure to be presented alongside its mean value.