Skritata ikonomika v Bălgarija (naselenie) Noemvri 2004 g (Centăr za izsledvane na demokracijata, 2004)
In the period November 18-29, 2004, Vitosha Research conducted a national representative survey of the "hidden economy" in the country, covering 959 respondents aged 18 and over. The survey employed the method of the face-to-face interview