Operation Domus Aurea, an ongoing investigation launched by the Guardia di Finanza in 2004, has estimated that over 6.000 apartments in the capital are currently rented without contract to students alone. Agents identified Nomentano, S. Lorenzo, Tiburtino and Prenestino as having the highest concentration of illegal student lets. A contemporary study by independent market research agency Istituto Scenari Immobiliari reported that rates for student lets had jumped by 47 per cent in the four years between 2001 and 2005, and showed no signs of slowing. According to the study, prices per room ranged from