"Data Trends" reports present summaries of research on mental health services for children and adolescents and their families. The article summarized in this "Data Trends" examines the equivalence of the BPI [Behavior Problem Index] across a sample of African American, Hispanic, and non-Hispanic White children drawn from the 1998 mother-child data file of the NLYS [National Longitudinal Survey of Youth]". The BPI is a 28-item instrument measuring a range of child behaviors. This widely used screening tool was developed "as a more concise and time-effective measure of child behavior and mental health problems than the CBCL [Child Behavior Checklist]". The authors conclude from this study that the "standard BPI subscales are valid principally for White children". Overall, the results indicate ethnicity-based differences in the BPI, when used both as a global measure and as a multidimensional measure of behavioral problems for children aged 4 and 14 years. This has important implications for both practice and research. Valid measurement plays an important role in children's mental health assessment, diagnosis, intervention, and treatment evaluation. Culturally biased screening tools may contribute to the well-documented problem of disparities in mental health care. As acknowledged by the authors, there is also a need for additional research with other populations that takes account of social, economic, and developmental variables in addition to cultural factors. Nevertheless, it is crucial that practitioners and researchers attend to cultural bias as a source of measurement error even when using instruments that have been standardized. Valid measures are essential. The authors propose that until "cultural considerations are integrated thoroughly into the initial phase of instrument development, there will be a need for more studies that investigate the cross-cultural validity of measures that are assumed to be equal." It is also important to recognize both the value and limitations of culture generalizations. Culture is dynamic, and increasing numbers of families belong to more than one ethnic group. Accurate assessment of children's mental health requires not just valid instruments, but also collaborative relationships between families and practitioners. The development of such relationships is likely to require a focus not just on problem behaviors, but also on child and family strengths. [This "Data Trends" presents a summary of: Spencer, Michael S., Fitch, D., Grogan Kaylor, A., & McBeath, B. (2005). The equivalence of the behavior problem index across U. S. ethnic groups. "Journal of Cross-Cultural Psychology," 36(5), 573-589.]