When filling out forms of various kinds, you would find it easier to be honest if you were asked to sign at the top rather than the bottom. When you sign at the bottom you’ve already stated whatever lies you’re going to tell.
But if you sign at the top, you’re burdened from the beginning by the moral weight of your pledge to be honest. This theory has been tested by having twenty thousand subjects fill out automobile insurance forms that they thought were real.
On the forms, clients were asked what their mileage was. Lower mileage got them lower premiums. Half the clients were asked to sign at the top; the other half were asked to sign at the bottom.
The theory was proved correct.
Source: Dan Ariely: Why we lie: the honest truth about dishonesty, Atlantic Online, May 29