EDIT, 4/18:  I'm closing the survey.  I'll post analysis and a better anonymized version of the raw data in a day or so.  236 people responded; thanks very much to all who did.

For survey participants curious about the calibration questions, the answers are:

Number of republics the USSR broke up into, following the output of the cold war: 15.

The year in which the global population reached 1 billion: 1804.

The average percentage of a watermelon's weight that comes from water: 92.