Data-driven decision making has been a common task in todays big data era, from simple choices such as finding a fast way for driving to work, to complex decisions on cancer treatment in healthcare, often supported by visual analytics. For various reasons (e.g., an ill-defined problem space, network failures or bias), visual analytics for sensemaking of data involves missingness (e.g., missing data and incomplete analysis), which can impact human decisions. For example, data, with missing records, can cost a business millions of dollars, and failing to recognize key evidence can put an innocent person into a sentence to death as a falsely convicted of murder. Being aware of missingness is critical to avoid such catastrophes. To achieve this, as an initial step, we present a framework of categorizing missingness in visual analytics from two perspectives: data-centric and human-centric. The former emphasizes missingness in three data-related categories: data composition, data relationship and data usage. The latter focuses on the human-perceived missingness at three levels: observed missingness, inferred missingness and ignored missingness. Based on the framework, we discuss possible roles of visualizations for handling missingness, and conclude our discussion with future research opportunities.
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