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Table 3 Relative contributions of within- and between-individual variance values, coefficients of within-individual variance (CVw) and between-individual variance (CVb), the number of days required for collecting food records necessary to estimate the true intake within 10 and 20% of the true mean, and the number of days required to ensure r = 0.9, 0.8 and 0.5 between observed and true mean intake

From: Variations in the estimated intake of acrylamide from food in the Japanese population

 Percentage contributions of variance components within-individualPercentage contributions of variance components between-individualVRMean intake
(μg/day)
CVwa
(%)
CVbb
(%)
D1
10%(days) c
D2
20%(days) c
D3
r = 0.9
(days)d
D4
r = 0.8 (days)d
D5
r = 0.5 (days)d
Men (n = 98)76.323.73.29.8079.144.0240601461
Women (n = 142)81.218.84.310.2183.039.9265661881
All (n = 240)79.820.23.910.0481.541.5255641671
  1. CVw, coefficient of within-individual variation; CVb, coefficient of between-individual variation; VR, ratio of within- to between- individual variance \( \left(\frac{{\hat{\sigma}}_w^2}{{\hat{\sigma}}_b^2}\right) \)
  2. a\( \mathrm{CVw}=\frac{\sqrt{{\hat{\sigma}}_w^2}}{\mathrm{mean}\ \mathrm{acrylamide}\ \mathrm{intake}}\times 100 \)
  3. b\( \mathrm{CVb}=\frac{\sqrt{{\hat{\sigma}}_b^2}}{\mathrm{mean}\ \mathrm{acrylamide}\ \mathrm{intake}}\times 100 \)
  4. cNumber of days needed to lie within specified % of the true means: D1.2 = (ZαCVw/E)2, where D = number of days needed per person, Zα = normal deviate (1.96), E = specific error admitted as a percentage of the true usual intake; 10% or 20%
  5. dNumber of days required to ensure r = 0.9 or 0.8 or 0.5 between observed and true mean intake: \( {\mathrm{D}}_{3,4,5}=\left[\frac{r^2}{\left(1-{r}^2\right)}\right]\times \mathrm{VR} \), where r = the unobservable correlation coefficient between the observed and true mean nutrient intakes of the individual