title: Development and validation of a food-based diet quality index for New Zealand adolescents.
abstract: BACKGROUND
  As there is no population-specific, simple food-based diet index suitable for examination of diet quality in New Zealand (NZ) adolescents, there is a need to develop such a tool. Therefore, this study aimed to develop an adolescent-specific diet quality index based on dietary information sourced from a Food Questionnaire (FQ) and examine its validity relative to a four-day estimated food record (4DFR) obtained from a group of adolescents aged 14 to 18 years.
  
  
  METHODS
  A diet quality index for NZ adolescents (NZDQI-A) was developed based on 'Adequacy' and 'Variety' of five food groups reflecting the New Zealand Food and Nutrition Guidelines for Healthy Adolescents. The NZDQI-A was scored from zero to 100, with a higher score reflecting a better diet quality. Forty-one adolescents (16 males, 25 females, aged 14-18 years) each completed the FQ and a 4DFR. The test-retest reliability of the FQ-derived NZDQI-A scores over a two-week period and the relative validity of the scores compared to the 4DFR were estimated using Pearson's correlations. Construct validity was examined by comparing NZDQI-A scores against nutrient intakes obtained from the 4DFR.
  
  
  RESULTS
  The NZDQI-A derived from the FQ showed good reliability (r = 0.65) and reasonable agreement with 4DFR in ranking participants by scores (r = 0.39). More than half of the participants were classified into the same thirds of scores while 10% were misclassified into the opposite thirds by the two methods. Higher NZDQI-A scores were also associated with lower total fat and saturated fat intakes and higher iron intakes.
  
  
  CONCLUSIONS
  Higher NZDQI-A scores were associated with more desirable fat and iron intakes. The scores derived from either FQ or 4DFR were comparable and reproducible when repeated within two weeks. The NZDQI-A is relatively valid and reliable in ranking diet quality in adolescents at a group level even in a small sample size. Further studies are required to test the predictive validity of this food-based diet index in larger samples.
authors.affiliation: Department of Human Nutrition, University of Otago, Dunedin 9054, New Zealand. jyh.wong@otago.ac.nz.
authors.forename: Jyh Eiin
authors.initials: JE
authors.lastname: Wong
authors.forename: Winsome R
authors.initials: WR
authors.lastname: Parnell
authors.forename: Anna S
authors.initials: AS
authors.lastname: Howe
authors.forename: Katherine E
authors.initials: KE
authors.lastname: Black
authors.forename: Paula M L
authors.initials: PM
authors.lastname: Skidmore
mesh_terms: D000293:Adolescent; D016497:Adolescent Health Services; D004032:Diet / Q000706:statistics & numerical data*; D015930:Diet Records; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D008297:Male; D009520:New Zealand; D018673:Nutrition Policy; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires