title: A bivariate measurement error model for nitrogen and potassium intakes to evaluate the performance of regression calibration in the European Prospective Investigation into Cancer and Nutrition study.
abstract: OBJECTIVE
  Within the European Prospective Investigation into Cancer and Nutrition (EPIC) study, the performance of 24-h dietary recall (24-HDR) measurements as reference measurements in a linear regression calibration model is evaluated critically at the individual (within-centre) and aggregate (between-centre) levels by using unbiased estimates of urinary measurements of nitrogen and potassium intakes.
  
  
  METHODS
  Between 1995 and 1999, 1072 study subjects (59% women) from 12 EPIC centres volunteered to collect 24-h urine samples. Log-transformed questionnaire, 24-HDR and urinary measurements of nitrogen and potassium intakes were analysed in a multivariate measurement error model to estimate the validity of coefficients and error correlations in self-reported dietary measurements. In parallel, correlations between means of 24-HDR and urinary measurements were computed. Linear regression calibration models were used to estimate the regression dilution (attenuation) factors.
  
  
  RESULTS
  After adjustment for sex, centre, age, body mass index and height, the validity coefficients for 24-HDRs were 0.285 (95% confidence interval: 0.194, 0.367) and 0.371 (0.291, 0.446) for nitrogen and potassium intakes, respectively. The attenuation factors estimated in a linear regression calibration model were 0.368 (0.228, 0.508) for nitrogen and 0.500 (0.361, 0.639) for potassium intakes; only the former was different from the estimate obtained using urinary measurements in the measurement error model. The aggregate-level correlation coefficients between means of urinary and 24-HDR measurements were 0.838 (0.637, 0.932) and 0.756 (0.481, 0.895) for nitrogen and potassium intakes, respectively.
  
  
  CONCLUSIONS
  This study suggests that 24-HDRs can be used as reference measurements at the individual and aggregate levels for potassium intake, whereas, for nitrogen intake, good performance is observed for between-centre calibration, but some limitations are apparent at the individual level.
authors.affiliation: Dietary Exposure Assessment Group, International Agency for Research on Cancer, Lyon, France.
authors.forename: P
authors.initials: P
authors.lastname: Ferrari
authors.forename: A
authors.initials: A
authors.lastname: Roddam
authors.forename: M T
authors.initials: MT
authors.lastname: Fahey
authors.forename: M
authors.initials: M
authors.lastname: Jenab
authors.forename: C
authors.initials: C
authors.lastname: Bamia
authors.forename: M
authors.initials: M
authors.lastname: Ocké
authors.forename: P
authors.initials: P
authors.lastname: Amiano
authors.forename: A
authors.initials: A
authors.lastname: Hjartåker
authors.forename: C
authors.initials: C
authors.lastname: Biessy
authors.forename: S
authors.initials: S
authors.lastname: Rinaldi
authors.forename: I
authors.initials: I
authors.lastname: Huybrechts
authors.forename: A
authors.initials: A
authors.lastname: Tjønneland
authors.forename: C
authors.initials: C
authors.lastname: Dethlefsen
authors.forename: M
authors.initials: M
authors.lastname: Niravong
authors.forename: F
authors.initials: F
authors.lastname: Clavel-Chapelon
authors.forename: J
authors.initials: J
authors.lastname: Linseisen
authors.forename: H
authors.initials: H
authors.lastname: Boeing
authors.forename: E
authors.initials: E
authors.lastname: Oikonomou
authors.forename: P
authors.initials: P
authors.lastname: Orfanos
authors.forename: D
authors.initials: D
authors.lastname: Palli
authors.forename: M
authors.initials: M
authors.lastname: Santucci de Magistris
authors.forename: H B
authors.initials: HB
authors.lastname: Bueno-de-Mesquita
authors.forename: P H M
authors.initials: PH
authors.lastname: Peeters
authors.forename: C L
authors.initials: CL
authors.lastname: Parr
authors.forename: T
authors.initials: T
authors.lastname: Braaten
authors.forename: M
authors.initials: M
authors.lastname: Dorronsoro
authors.forename: T
authors.initials: T
authors.lastname: Berenguer
authors.forename: B
authors.initials: B
authors.lastname: Gullberg
authors.forename: I
authors.initials: I
authors.lastname: Johansson
authors.forename: A A
authors.initials: AA
authors.lastname: Welch
authors.forename: E
authors.initials: E
authors.lastname: Riboli
authors.forename: S
authors.initials: S
authors.lastname: Bingham
authors.forename: N
authors.initials: N
authors.lastname: Slimani
mesh_terms: D000328:Adult; D000368:Aged; D002138:Calibration / Q000592:standards*; D004032:Diet; D015930:Diet Records; D004034:Diet Surveys; D005060:Europe; D005260:Female; D006801:Humans; D016014:Linear Models; D016015:Logistic Models; D008297:Male; D018977:Micronutrients / Q000008:administration & dosage / Q000652:urine; D008875:Middle Aged; D009584:Nitrogen / Q000008:administration & dosage* / Q000652:urine; D011188:Potassium / Q000008:administration & dosage* / Q000652:urine; D011446:Prospective Studies; D012016:Reference Values; D015203:Reproducibility of Results
chemical_list: D018977:Micronutrients; D009584:Nitrogen; D011188:Potassium