“…According to recent publications, non-self-reported ethnicity can be based on lifestyle [ 34 ], surname [ 35 ], and residence [ 36 , 37 , 38 , 39 , 40 ], but not on explicitly defined racial characteristics [ 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. Health care staff members [ 48 ], officers [ 34 ], survey interviewers (with or without the support of a Roma community leader [ 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 ]), and parents of children [ 59 , 60 ] can perform this classification. Furthermore, the combination of self-reporting and a decisive external classification is also in practice [ 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ].…”