Milan, January 16 - The Calabrian mafia 'Ndrangheta and the Neapolitan Camorra together rake in nearly 70% of all organized-crime revenues in Italy, according to a study commissioned by the Italian interior ministry and presented at a conference in Milan on Wednesday. The study, called the Mafia Presence Index (IPM), provides an assessment of mafia presence across Italy and was carried out by the Transcrime Inter-university Centre of the Universita' Cattolica del Sacro Cuore in Milan, headed by professor Ernesto Savona. The study found that Sicily's Cosa Nostra ranked a distant third to the 'Ndrangheta and Camorra in terms of revenues from organized crime, garnering 18% of the national total. Roughly 50% of 'Ndrangheta's revenue is raised in northern Italy, the study found, whereas other mafia groups tend to concentrate business activities in their territory of origin. 'Ndrangheta receives an estimated 23% of its revenues from its native Calabria, but nets 21% and 16% in Piedmont and Lombardy, respectively. It also has significant business activities in Emilia-Romagna, Lazio and Liguria. In an examination of 19,987 assets seized from mafia suspects from 1983 to 2011, more than half - or 52.3% - were real estate properties. Other physical assets and equities accounted for 18.4% and 8.7% of the total, respectively. In terms of businesses, criminals preferred to invest in limited companies, which made up 46% of total business investments. Only 2% of mafia-linked business investments were made in listed companies. The mafia groups tended to take stakes in low technology enterprises, especially wholesale and retail firms, which constituted 29.4% of the total and construction, which made up 28.8%. Crime bosses' third favorite category was hospitality. Hotels and restaurants together made up 10.5% of all mafia-linked businesses seized.