The malocclusion impact questionnaire (MIQ): Cross-sectional validation in a group of young people seeking orthodontic treatment in New Zealand

The aim of the study was to test the validity of the Malocclusion Impact Questionnaire (MIQ) in a NZ sample and to evaluate possible cross-cultural differences in MIQ data between a NZ and a UK sample. A cross-sectional, non-random sample of young people, aged 10-16 years, attending their first appointment at the orthodontic clinic of New Zealand's National Centre for Dentistry were asked to complete a questionnaire. This consisted of the 17 item MIQ, the short form CPQ 11-14 -ISF16 and two global questions. Some basic demographic and clinical data were collected. Sixty-six participants completed the questionnaire; however, the data for 2 were excluded due to the number of incomplete responses. MIQ was found to have excellent internal consistency (Cronbach's alpha 0.924), good construct validity (Spearman's rho, 0.661 global Q1 'Overall, how much do your teeth bother you?'; 0.583 global Q2 'Overall, how much do your teeth affect your life?'). MIQ also demonstrated good criterion validity with CPQ 11-14 -ISF16 (Pearson rho, 0.625). The Rasch analysis confirmed that the questionnaire performed similarly and there was no differential item functioning between the two populations. The main differences between the samples were that the young people in NZ were less concerned about their malocclusion and reported lower item-impact scores compared with the young people in the UK.