title: Intra-individual variation in urinary iodine concentration: effect of statistical correction on population distribution using seasonal three-consecutive-day spot urine in children.
abstract: OBJECTIVE
  To determine the effect of statistical correction for intra-individual variation on estimated urinary iodine concentration (UIC) by sampling on 3 consecutive days in four seasons in children.
  
  
  METHODS
  School-aged children from urban and rural primary schools in Harbin, Heilongjiang, China.
  
  
  METHODS
  748 and 640 children aged 8-11 years were recruited from urban and rural schools, respectively, in Harbin.
  
  
  METHODS
  The spot urine samples were collected once a day for 3 consecutive days in each season over 1 year. The UIC of the first day was corrected by two statistical correction methods: the average correction method (average of days 1, 2; average of days 1, 2 and 3) and the variance correction method (UIC of day 1 corrected by two replicates and by three replicates). The variance correction method determined the SD between subjects (Sb) and within subjects (Sw), and calculated the correction coefficient (Fi), Fi=Sb/(Sb+Sw/di), where di was the number of observations. The UIC of day 1 was then corrected using the following equation:[Formula: see text]
  
  
  RESULTS
  The variance correction methods showed the overall Fi was 0.742 for 2 days' correction and 0.829 for 3 days' correction; the values for the seasons spring, summer, autumn and winter were 0.730, 0.684, 0.706 and 0.703 for 2 days' correction and 0.809, 0.742, 0.796 and 0.804 for 3 days' correction, respectively. After removal of the individual effect, the correlation coefficient between consecutive days was 0.224, and between non-consecutive days 0.050.
  
  
  CONCLUSIONS
  The variance correction method is effective for correcting intra-individual variation in estimated UIC following sampling on 3 consecutive days in four seasons in children. The method varies little between ages, sexes and urban or rural setting, but does vary between seasons.
authors.affiliation: Key Laboratory of Etiology and Epidemiology, Education Bureau of Heilongjiang Province and Ministry of Health, Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Harbin, People's Republic of China.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Ji
authors.affiliation: Key Laboratory of Etiology and Epidemiology, Education Bureau of Heilongjiang Province and Ministry of Health, Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Harbin, People's Republic of China.
authors.forename: Peng
authors.initials: P
authors.lastname: Liu
authors.affiliation: Key Laboratory of Etiology and Epidemiology, Education Bureau of Heilongjiang Province and Ministry of Health, Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Harbin, People's Republic of China.
authors.forename: Zhenqi
authors.initials: Z
authors.lastname: Sun
authors.affiliation: Key Laboratory of Etiology and Epidemiology, Education Bureau of Heilongjiang Province and Ministry of Health, Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Harbin, People's Republic of China.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Su
authors.affiliation: Key Laboratory of Etiology and Epidemiology, Education Bureau of Heilongjiang Province and Ministry of Health, Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Harbin, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Key Laboratory of Etiology and Epidemiology, Education Bureau of Heilongjiang Province and Ministry of Health, Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Harbin, People's Republic of China.
authors.forename: Yanhui
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Key Laboratory of Etiology and Epidemiology, Education Bureau of Heilongjiang Province and Ministry of Health, Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Harbin, People's Republic of China.
authors.forename: Dianjun
authors.initials: D
authors.lastname: Sun
mesh_terms: D017677:Age Distribution; D002648:Child; D002681:China; D003710:Demography; D005260:Female; D006801:Humans; D007455:Iodine / Q000652:urine*; D008297:Male; D012424:Rural Population / Q000706:statistics & numerical data; D012621:Seasons; D017678:Sex Distribution; D014505:Urban Population / Q000706:statistics & numerical data
chemical_list: D007455:Iodine
keywords: intraindividual; shool-aged children; statistical correction; urinary iodine concentration