Designing bar graphs: orientation matters

We investigated whether recent discoveries about the cognitive representation of numbers would predict performance in a graph comprehension task. Participants decided verbally whether statements of the form ‘A>B’ were correct descriptions of subsequently presented bar graphs. We observed longer decision times for horizontal compared to vertical bar graphs and for negative compared to positive number graphs. Comprehension was faster when the spatial layout of magnitude information matched an internal ‘mental number line’. These results show that the design of graphs can benefit from research into number representations.