It's possible.
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> Mafia crime is 7% of GDP in Italy, group reports
Original report
The source is SOS Impresa, an association that supports businesses threatened by the Mafia. Thus they have a vested interest in inflating the number.
It's highly doubtful that there are meaningful statistics on a criminal organization that seeks to conceal it's activities. The SOS Impresa source is the most recent attempt at this.