Validity and reliability of an FFQ for use with adolescents in Ho Chi Minh City, Vietnam. 
The present study evaluates the reliability and validity of an FFQ designed for use with adolescents in urban Vietnam.  A cohort study was conducted between December 2003 and June 2004.  The FFQ was administered three times over a 6-month period (FFQ 1-3) and nutrient intakes were compared to those obtained from four 24 h recalls collected over the same period (24 h recalls 1-4) using crude, energy-adjusted and de-attenuated correlation coefficients.  The level of agreement between the two measurements was also evaluated with Bland-Altman analysis.  The percentage of nutrient intakes classified within one quintile, as well as quadratic-weighted kappa statistics, were calculated.  Ho Chi Minh City, Vietnam.  A total of 180 students were recruited in three junior high schools.  Coefficients ranged from 0.22 for retinol to 0.78 for fibre for short-term reliability, and from 0.30 for retinol to 0.81 for zinc for long-term reliability.  Coefficients for nutrient intakes between the mean of the three FFQ and mean of four 24 h recalls were mostly around 0.40, but higher for energy-adjusted nutrients.  After allowing for within-person variation, the mean coefficient was 0.52 for macronutrients and 0.46 for micronutrients.  There were a relatively high proportion of nutrient intakes classified within one quintile and a small number grossly misclassified.  Kappa values shows 'fair' to 'good' agreement for all food/nutrient categories, while the Bland-Altman plots indicated that the FFQ is accurate in assessing nutrient intake at a group level.  This newly developed FFQ is a valid tool for measuring nutrient intake in adolescents in urban Vietnam.