“…Of the 50 studies that used interviewer-administered questionnaires, 64.0% (n = 32) reported that the interviewers received training [8, 10, 11, 14, 22, 24, 25, 27, 29, 33, 34, 38-40, 42-46, 53, 54, 56-58, 60, 63-66, 68-70]. The remaining 19% of studies (n = 12) used email and mail questionnaires and online panels [13,16,18,26,35,36,48,50,55,61,62,67].…”