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Activity Number: 692
Type: Contributed
Date/Time: Thursday, August 8, 2013 : 10:30 AM to 12:20 PM
Sponsor: Section on Statistics in Epidemiology
Abstract - #309575
Title: Piecewise Spline to Compare Weight Gain Pattern Before and After Diagnosis of Asthma of Children Ages Less Than 5 Years
Author(s): Md Jobayer Hossain and Li Xie*+ and Weili Lai and Iman Sharif and H Timothy Bunnell and Timothy T. Wysocki
Companies: Nemours Biomedical Research A.I. DuPont Children Hospital and Johns Hopkins Bloomberg School of Public Health and University of Delaware and A I dupont Children Hospital and Nemours Biomedical Research and Nemours Biomedical Research A.I. DuPont Children Hospital
Keywords: Piecewise spline ; weight gain ; BMIz ; estimated variance
Abstract:

weight-for-length (age < 2 years) and BMI (>= 2 years)are commonly used measures of weight gain. We used standardized scores (BMIz) of these two measures of 1173 asthmatic children of ages 0-5 years to compare the pattern of weight gain before and after diagnosis of asthma. Lowess smoothed curve showed a linear increase in BMIz over time but with a different slopes before and after diagnosis of asthma among these children. A piecewise linear mixed effect model with a knot at the age of asthma diagnosis showed a significant difference (p< .001) in the mean trend of BMIz between before and after diagnosis. The slope showed a shallow increase(p=0.79) in BMIz before diagnosis of asthma, while it showed a sharp increase (p< .0001) after diagnosis. The post-diagnosis rate of increase in BMIz is more than 20 times as high as it is during pre-diagnosis period. The estimated variance of time slope during pre-asthma diagnosis is about 3 times as high as it is during post-asthma diagnosis. About 51% children were expected to have an increase in BMIz during the post-diagnosis period, while an about 82% children were expected to have an increase after diagnosis.


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