title: Within-person variance in biochemical indicators of iron status: effects on prevalence estimates.
abstract: The effect of within-person variance on prevalence estimates from population distributions based on a single measurement was examined for hematologic and iron-status indicators collected in the Hispanic Health and Nutrition Examination Survey (HHANES). Within-person to between-person variance ratios (W:Bs) were estimated for 11 indicators by using data from 80 persons who provided blood twice in HHANES. Distributions of selected iron-status indicators from 20-44-y-old Mexican American females from HHANES were adjusted for within-person variance by using the W:B estimates, and prevalences of low values based on the original and adjusted distributions were compared. W:B were less than 1 for the majority of the indicators. Nonetheless, prevalences of low values from the original distributions were inflated when commonly used cutoff values were applied. Within-person variance in serum analytes needs to be controlled when the prevalence of a condition in populations is assessed.
authors.affiliation: Division of Health Examination Statistics, National Center for Health Statistics, Hyattsville, MD 20782.
authors.forename: A C
authors.initials: AC
authors.lastname: Looker
authors.forename: C T
authors.initials: CT
authors.lastname: Sempos
authors.forename: K A
authors.initials: KA
authors.lastname: Liu
authors.forename: C L
authors.initials: CL
authors.lastname: Johnson
authors.forename: E W
authors.initials: EW
authors.lastname: Gunter
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D000747:Anemia, Hypochromic / Q000097:blood / Q000453:epidemiology*; D004912:Erythrocytes / Q000032:analysis; D005260:Female; D006306:Health Surveys; D006454:Hemoglobins / Q000032:analysis; D006630:Hispanic or Latino; D006801:Humans; D007501:Iron / Q000097:blood; D015596:Nutrition Assessment; D011524:Protoporphyrins / Q000032:analysis; D014168:Transferrin / Q000032:analysis; D014481:United States
chemical_list: D006454:Hemoglobins; D011524:Protoporphyrins; D014168:Transferrin; D007501:Iron