title: Misclassification associated with measurement error in the assessment of dietary intake.
abstract: OBJECTIVE
  Dietary assessment has been used for certification to receive food supplements or other nutrition services and to provide feedback for educational purposes. The proportion of individuals correctly certified as eligible is a function of the amount of error that exists in the dietary measures and the level of dietary intake used to establish eligibility. Whether individuals are correctly counselled to increase or decrease the consumption of selected foods or nutrients is a function of the same factors. It is not clear, however, what percentage of individuals would be correctly classified under what circumstances. The objective of this study is to demonstrate the extent to which measurement error and eligibility criteria affect the accuracy of classification.
  
  
  METHODS
  Hypothetical distributions of dietary intake were generated with varying degrees of measurement error. Different eligibility criteria were applied and the expected classification rates were determined using numerical methods.
  
  
  METHODS
  Simulation study.
  
  
  RESULTS
  Cut points of dietary intake at decreasing levels below the 50th percentile of true intake were associated with lower sensitivity and predictive value positive rates, but higher specificity and predictive value negative rates. The correct classification rates were lower when two cut points of dietary intake were used. Using a single cut point that was higher than the targeted true consumption resulted in higher sensitivity but lower predictive value positive, and lower specificity but higher predictive value negative.
  
  
  CONCLUSIONS
  Current methods of dietary assessment may not be reliable enough to attain acceptable levels of correct classification. Policy-makers and educators must consider how much misclassification error they are willing to accept and determine whether more intensive methods are necessary.
authors.affiliation: Departments of Behavioral Science, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard - Box 243, TX 77030, USA. cdemoor@mdanderson.org
authors.forename: Carl
authors.initials: C
authors.lastname: De Moor
authors.forename: Tom
authors.initials: T
authors.lastname: Baranowski
authors.forename: Karen W
authors.initials: KW
authors.lastname: Cullen
authors.forename: Theresa
authors.initials: T
authors.lastname: Nicklas
mesh_terms: D015982:Bias; D003198:Computer Simulation; D004032:Diet / Q000706:statistics & numerical data*; D004608:Eligibility Determination / Q000592:standards*; D002149:Energy Intake; D005522:Food Services; D006801:Humans; D015596:Nutrition Assessment; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity