A small sample of known burglars were interviewed also to determine if appearance of an identification number on an item deterred them from stealing it. Data were collected for 8 years: 4 years during which households participated in the marking program and 4 years previous to their participation. Results did not support the theory that marking valuables made them less attractive to thieves. Most of the thieves interviewed said that they had seen marked valuables in the course of their activities, and about half admitted being aware of the significance of the identification number. Most said the mere presence of the number was no deterrent. Data collected from households supported this. During the observation period, the incidence of burglary increased slightly among households participating in the program (while it decreased slightly among nonparticipating household). Furthermore, the survey showed that households with marked goods had no significantly better chance of recovering stolen goods that were regained by police. Another problem with Operation Marking is notable. Many valuables, such as jewelry and silverware, are too small to mark.