title: Validity and systematic error in measuring carotenoid consumption with dietary self-report instruments.
abstract: Vegetables and fruits are rich in carotenoids, a group of compounds thought to protect against cancer. Studies of diet-disease associations need valid and reliable instruments for measuring dietary intake. The authors present a measurement error model to estimate the validity (defined as correlation between self-reported intake and "true" intake), systematic error, and reliability of two self-report dietary assessment methods. Carotenoid exposure is measured by repeated 24-hour recalls, a food frequency questionnaire (FFQ), and a plasma marker. The model is applied to 1,013 participants assigned between 1995 and 2000 to the nonintervention arm of the Women's Healthy Eating and Living Study, a randomized trial assessing the impact of a low-fat, high-vegetable/fruit/fiber diet on preventing new breast cancer events. Diagnostics including graphs are used to assess the goodness of fit. The validity of the instruments was 0.44 for the 24-hour recalls and 0.39 for the FFQ. Systematic error accounted for over 22% and 50% of measurement error variance for the 24-hour recalls and FFQ, respectively. The use of either self-report method alone in diet-disease studies could lead to substantial bias and error. Multiple methods of dietary assessment may provide more accurate estimates of true dietary intake.
authors.affiliation: Division of Biostatistics, University of California, La Jolla, CA, USA. loki@math.ucsd.edu
authors.forename: Loki
authors.initials: L
authors.lastname: Natarajan
authors.forename: Shirley W
authors.initials: SW
authors.lastname: Flatt
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Sun
authors.forename: Anthony C
authors.initials: AC
authors.lastname: Gamst
authors.forename: Jacqueline M
authors.initials: JM
authors.lastname: Major
authors.forename: Cheryl L
authors.initials: CL
authors.lastname: Rock
authors.forename: Wael
authors.initials: W
authors.lastname: Al-Delaimy
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Thomson
authors.forename: Vicky A
authors.initials: VA
authors.lastname: Newman
authors.forename: John P
authors.initials: JP
authors.lastname: Pierce
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000517:prevention & control; D002338:Carotenoids / Q000008:administration & dosage* / Q000097:blood; D015930:Diet Records; D005260:Female; D006801:Humans; D011939:Mental Recall; D015233:Models, Statistical; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires
chemical_list: D002338:Carotenoids