Skritata ikonomika v Bălgarija (naselenie) Mart 2003 g (Centăr za izsledvane na demokracijata, 2003)
In the period January 23 - February 02, 2003, Vitosha Research conducted a national representative survey of the "hidden economy" in the country, covering 1107 respondents aged 18 and over. The survey employed the method of the face-to-face interview