If you read any good text on dataviz, like Tufte, Few, or Cairo, you will, at some point, come across a discussion of the cognitive aspects of data visualization (the latter two devoting entire chapters to this topic). This will likely include a discussion of the most elemental ways to encode information visually, and their respective accuracies when quantity is interpreted from them, usually referencing the work of Cleveland & McGill [PDF].
Mulling over the veracity of my brief mention of the visual ways of encoding quantity in my recent talk, and also recently re-reading Nathan Yau's discussion of the aforementioned paper, I got to thinking about just how different the accuracy of interpretation between the different encodings might be.
I am not a psychologist or qualitative researcher, but given the above quickly put together a simple test of 7 questions in Google Docs, to examine the accuracy of interpreting proportional quantities when encoded visually; and I humbly request the favour of your participation. If there are enough responses I will put together what analysis is possible in a future post (using the appropriate visualization techniques, of course).
Apologies in advance for the grade-school wording of the questions, but I wanted to be as clear as possible to ensure consistency in the results. Thanks so much in advance for contributing! Click below for the quiz:
EDIT: The quiz will now be up indefinitely on this page.