One possibility is that such differences reflect financial inequalities, e.g., that poorer black families in both countries are unable to afford or access services so that black children are underdiagnosed and undertreated. According to this hypothesis, one would expect a low prevalence and treatment rate for children in low-income families as well as for black children. This is unlikely for several reasons. First, in the United Kingdom, ADHD is more prevalent in children of low-income families but less prevalent among black children. Second, the significant increase in the rate of treatment for low-income families in the United States has not been matched by a corresponding increase in treatment rates for black children. Third, difficulties accessing services should not have affected diagnoses in the British study, which involved interviews with children and parents and mailed questionnaires for teachers, regardless of whether they had had any contact with services.