Distribution of studied subjects regarding age and gender Age group (month) Boys (n,%) Girls (n,%) Total (n,%) p 0-<12 6 (46.2) 7 (53.8) 13 (3.2) =0.589 12-<24 55 (59.8) 37 (40.2) 92 (22.7) 24-<36 58 (54.2) 49 (45.8) 107 (26.3) 36-<48 62 (55.9) 49 (44.1) 111 (27.3) 48-<60 40 (48.2) 43 (51.8) 83 (20.5) Tổng 221 (54.4) 185 (45.6) 406 (100, 0) 8 Remark: More boys than girls participated in the study.