A P R E D I C T I O N M O D E L T O P R E V E N T A B N O R M A L W E I G H T I N C H I L D H O O D αBMI tot Represents the mean change in BMI of the population from the age of 1 year until the age of 4 years. Based on these α tot values the expected value of the PI or BMI at a certain age for an individual child can be calculated according to the for-‐ mulas: PIe = (-‐0.64x + 1.29) * t + x Where -‐0.64x + 1.29 = αPI tot , x = PI at birth and t = the decimal age, 0 < t ≤ 1 BMIe = (-‐0.18x + 2.72) * t + x Where -‐0.18x + 2.72 = αBMI tot, x = BMI at the age of 1 year and t = the decimal age, 1 < t ≤ 4 The mean expected PI of all measurements is: 2.28 (with a standard deviation (SD) of 0.075) at the age of 1 year. The mean expected BMI of all measurements is: 15.50 (SD: 0.436) at the age of 4 years. For example, a child with a birth weight of 4 kg and a birth length of 51 cm, has a corresponding PI at birth of 3. According to the formula, it is to be expected that this infant will have a PI at the age of 1 year of 2.37 ((-‐0.64 * 3 + 1.29) * 1 + 3 = 2.37). With a given SD of 0.075 the range of expectation of the PI with a confidence interval of 2 SD is between 2.22 and 2.52. In the same way the BMI at the age of 4 years can be estimated by knowing the BMI at the age of 1 year. For example, a child with a weight at the age of 1 year of 9 kg and a length of 75 cm has a corre-‐ sponding BMI at the age of 1 year of 16. According to the formula, it is to be ex-‐ pected that this child will have a BMI of 15.36 at the age of 4 years ((-‐0.18 * 16 + 2.72) * 4 + 16 = 15.36). With given SD of 0.436 the range of expectation of the BMI with a confidence interval of 2 SD is from 14.49 to 16.23. The mean difference between the measured and expected PI values at the age of 1 year is -‐0.002 (SD = 0.22). The mean difference between the measured and ex-‐ pected BMI values at the age of 4 years is 0.003 (SD = 1.35). In Figure 3, the difference between the measured PI value and the estimated PI value at the age of 1 year is plotted against the PI at birth (as calculated above). In Figure 4, the difference between the measured BMI value and the estimated BMI value at the age of 4 years is plotted against the BMI at the age of 1 year (as calcu-‐ lated above). 81
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