Ben Vollaard, an economist at the University of Tubingen, has been running an experiment on his colleagues. They have a departmental refrigerator that’s stocked with soda—profs and grad students can help themselves, but they have to mark what they take; they get a bill from the department’s secretaries every couple of months. Vollaard’s experiment? He’s alternately provided and removed a pen by the tally sheet. When the pen was removed, he reports, “The theft rate went up from a mere one out of 14 cans to no less than one out of three cans once the pen was taken away. This amounted to a 370% increase in the theft rate.”

https://www.oreilly.com/ideas/dont-underestimate-easy-when-it-comes-to-data-access