title: Development of a performance-rating scale for a nutrition knowledge test developed for adolescents.
abstract: OBJECTIVE
  The objectives of the present study were to (i) develop and validate a norm-referenced performance-rating scale to interpret a nutrition knowledge test developed for urban adolescents and (ii) develop a prototype for other researchers to follow when developing nutrition knowledge tests.
  
  
  METHODS
  For norm development the nutrition knowledge test (questionnaire) was administered to a sample representative of the questionnaire target group, referred to as the norm group. These included 512 adolescents in grades 8 (n 158), 10 (n 149) and 12 (n 205) at three randomly selected schools in Soweto and Johannesburg. The performance scores (in percentages) obtained by the norm group were transformed to Z-scores which were categorised into stanines using established Z-score cut-off points. For validation purposes the questionnaire was completed by 148 volunteers: sixty university dietetics students, nineteen non-nutrition university students and sixty-nine primary-school teachers.
  
  
  RESULTS
  As required of an ideal norm group, the Z-scores formed a normal distribution (a bell-shaped curve). To facilitate interpretation of the results, the Z-score cut-off points for these categories were transformed back to performance scores (percentages) so that the performance of a testee could be interpreted directly from his/her performance in percentage. As is recommended, the nine stanine categories were reduced to five: very poor, fair/below average, good/average, very good/above average and excellent. The discriminatory validity of the norms was substantiated by showing that groups with known nutrition knowledge levels were rated appropriately and that the performance ratings of these groups differed significantly, with university dietetics students scoring 98.3%, primary-school teachers 20.3% and non-nutrition university students 31.6%.
  
  
  CONCLUSIONS
  The norm-referenced performance-rating scale can be used with confidence to interpret the performance score achieved by a testee on the nutrition knowledge test developed for urban adolescents in South Africa. The methodology used in the study serves as a prototype for other researchers who are developing knowledge tests.
authors.affiliation: CDL Unit, South African Medical Research Council, PO Box 19070, Cape Town, 7505, South Africa.
authors.forename: Lindiwe
authors.initials: L
authors.lastname: Whati
authors.forename: Marjanne
authors.initials: M
authors.lastname: Senekal
authors.forename: Nelia P
authors.initials: NP
authors.lastname: Steyn
authors.forename: Carl
authors.initials: C
authors.lastname: Lombard
authors.forename: Johanna
authors.initials: J
authors.lastname: Nel
mesh_terms: D000293:Adolescent; D000328:Adult; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D016011:Normal Distribution; D009747:Nutritional Physiological Phenomena; D052756:Nutritional Sciences; D012016:Reference Values; D013019:South Africa; D011795:Surveys and Questionnaires; D014505:Urban Population; D055815:Young Adult