To avoid this problem, the study exploited the variation created by the fact that the titling program was carried out in different stages. It began in certain neighborhoods in Lima and in subsequent years spread in a staggered pattern to other neighborhoods of the capital and to other cities. Rather than compare those households that obtained property titles with those that did not, the study compared the number of hours worked in the year 2000 by households eligible to obtain title (whether or not they actually obtained it) in neighborhoods already reached by the program, with hours worked by those eligible in neighborhoods the program had not yet reached. As a precaution, the author also compared the difference in working hours between those ineligible to obtain title (because they possessed formal title before the program began) in neighborhoods reached by the program and those ineligible in neighborhoods not yet reached, and subtracted this difference from the first.

Philip Mirowski & Dieter Plehwe (eds.), The Road from Mont Pèlerin, loc. 1938