A 3D swivel bar chart has primary bars with associated secondary bars shown in a condensed form, such as along the z-axis hidden behind a corresponding primary bar. When a primary bar is selected, associated secondary bars swivel out from the z-axis to the front plane. When deselected, the secondary bars swivel back to the z-axis. The user can see additional information is tied to a bar without cluttering the presentation. For an application involving evaluation of a cognitive system, the primary bars can represent confidence levels for candidate answers to a natural language question. The chart includes a legend which displays a particular result when the corresponding primary bar is selected. When a label in the legend is selected, the visualization is augmented with explanatory information pertaining to the particular result, such as evidence extracted from corpora used by the cognitive system to arrive at the result.