A New Zealand study has shown that the ethnic classification method used in research has a substantial impact on reported outcomes in adolescent mental health. The study used a nationally representative sample of 8275 adolescents aged 12-18 years, of whom 55% were female and 32% multi-ethnic. The impact of 5 ethnic classification methods on 3 mental health outcomes were investigated: overall psychosocial difficulties, deliberate self-harm, and suicide attempts. Reported outcomes within the same nominal ethnic group varied by an effect size of up to 0.12, and the reported magnitude of difference between nominal ethnic groups varied by an effect size of up to 0.25. The authors concluded that their study highlighted the importance of criticality and transparency in research involving ethnicity data.
