  Establishing trust with readers is an important first step in visual data
communication. But what makes a visualization trustworthy? Psychology and
behavioral economics research has found processing fluency (i.e., speed and
accuracy of perceiving and processing a stimulus) is central to perceived
trust. We examine the association between processing fluency and trust in
visualizations through two empirical studies. In Experiment 1, we tested the
effect of camouflaging a visualization on processing fluency. Participants
estimated the proportion of data values within a specified range for six
camouflaged visualizations and one non-camouflaged control; they also reported
their perceived difficulty for each of the visualizations. Camouflaged
visualizations produced less accurate estimations compared to the control. In
Experiment 2, we created a decision task based on trust games adapted from
behavioral economics. We asked participants to invest money in two hypothetical
companies and report how much they trust each company. One company communicates
its strategy with a camouflaged visualization, the other with a controlled
visualization. Participants tended to invest less money in the company
presenting a camouflaged visualization. Hence, we found support for the
hypothesis that processing fluency is key to the perception of trust in visual
data communication.
