For example, a questionnaire on the number of headaches people experience in one week was given to two different groups of subjects. One group had to indicate whether the number was 1-5, 6-10, 11-15, and so on, while the other was presented with the numbers broken down into 1-3, 4-6, 7-9, etc. The first group reported many more headaches than the second. Moreover, almost everyone is influenced by the two end points of a scale, tending to pick a number that is near the middle.
Excerpt from: Irrationality: The enemy within by Stuart Sutherland