Quantile regression, a method used to estimate conditional quantiles of a set of data ( X, Y ), was popularized by Koenker and Bassett (1978). For a particular quantile q , the q th quantile estimate of Y given X = x can be found using an asymmetrically-weighted, absolute-loss criteria. This form of regression is considered to be robust, in that it is less affected by outliers in the data set than least-squares regression. However, like standard L 1 regression, this form of quantile regression can still be affected by multiple outliers. In this thesis, we propose a method for improving robustness in quantile regression through an application of Scott's L 2 Estimation (2001). Theoretic and asymptotic results are presented and used to estimate properties of our method. Along with simple linear regression, semiparametric extensions are examined. To verify our method and its extensions, simulated results are considered. Real data sets are also considered, including estimating the effect of various factors on the conditional quantiles of child birth weight, using semiparametric quantile regression to analyze the relationship between age and personal income, and assessing the value distributions of Major League Baseball players.

Although very low birth weight preterm (VLBW) infants with grade 3,4 retinopathy of prematurity (ROP) are at high risk for unfavorable visual outcomes, the middle school vision motor integration (VMI) skills and cognitive outcome scores of these children remain largely unknown. Data for 323 very VLBW survivors of the Multicenter Randomized Indomethacin IVH Prevention Trial (BW 600 1250 g) were analyzed to test the hypothesis that grades 3, 4 ROP would be an important predictor of cognitive and VMI skills. 3 subgroups were evaluated: ROP negative (N = 163), ROP grades 1,2 (N = 137) and ROP grades 3,4 (N = 23) were evaluated prospectively at 12 years of age with a neurocognitive battery. High-resolution volumetric MRI scans were quantified for 40 of the study subjects, and occipital brain volumes were correlated with Beery VMI scores. Children with ROP 3-4 had [arrow up - increased] vision impairment and lower test scores. Whole brain volumes were significantly less for children with any grade of ROP (p = 0.02), occipital white matter volumes tended to be less for the same study subjects (p = 0.08) and both total occipital brain volumes and occipital white matter volumes were significantly correlated with Beery VMI scores (r=0.610, p = 0.009 and r = 0.652, p =0.005, respectively). Prematurely-born children with a history of grade 3-4 ROP continue to have [arrow up - increased] vision impairment, special needs and lower performance on cognitive, language and visual motor integration scores at age 12 years. Both whole occipital brain volumes and occipital white matter volumes were predictive of VMI scores for children with ROP. (supp by NS 27116)

The purpose of this study was to determine the effect of posttraumatic stress disorder (PTSD), diagnosed prospectively during pregnancy, on the occurrence of low birthweight (<2500 grams) and preterm delivery (<37 weeks gestational age). A cohort of 1362 women was recruited from prenatal care visits and screened for depression, panic disorder, posttraumatic stress disorder, and substance use. Current episodes of PTSD were assessed using the MINI International Neuropsychiatric Interview. Pregnancy outcomes were abstracted from hospital records after delivery, and the data were analyzed using logistic regression. Two hundred sixty two women (33%) were lost to follow-up due to unavailable medical records, leaving 1100 women in the final analyses. Among these 1100 women, 31 (3%) were found to have PTSD during pregnancy. Substance use in pregnancy, panic disorder, major and minor depressive disorders, and prior preterm delivery were significantly associated with PTSD in the sample, while age, language spoken, and race were not. Low birthweight (LBW) was present in 6.5% of sampled women and was not significantly associated with a diagnosis of PTSD in pregnancy when adjusting for potential confounders. However, LBW was significantly associated with minor depressive disorder OR= 1.82 (CI=1.01, 3.29). Preterm delivery occurred in 7.0% of those without and 16.1% of those with PTSD (p=0.055). Because prior preterm delivery data were not available for 33% of women with PTSD, this variable was included only in secondary analyses. However, the association between PTSD and preterm delivery depended on this variable, with OR= 2.82 (0.95, 8.38) before controlling for prior preterm delivery and OR=3.35 (1.04, 10.85) after controlling for prior preterm delivery. These data suggest that a possible association of PTSD and preterm delivery was limited by the low rates of PTSD in this cohort and the inability to control for all confounders. Taken together, these findings provide limited support for the hypothesized association between PTSD and preterm delivery and no support for an association of PTSD with LBW.

Thesis (D.P.H.)--University of Alabama at Birmingham, 2007. / Title from PDF title page (viewed on Feb. 19, 2010). Includes bibliographical references.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

No description available.

This dissertation consists of three essays examining the determinants of child developmental outcomes using the Canadian National Longitudinal Survey of Children and Youth (NLSCY). The first essay estimates the relationship between birth weight and cognitive and behavioral outcomes for children aged 0 to 13. Using family fixed effects models to control for household heterogeneity, I find that every ounce counts; additional birth weight for infants born weighing less than 2,500 grams (low birth weight infants) is related to better outcomes for measures of math ability, pro-social behavior and property offense. Additional birth weight for those born weighing 2,500 grams or more is related to higher scores of motor and social development and verbal competence for young children. The second essay, using a sample of Canadian boys and girls aged 10 to 15 in dual-earner families, finds that parental work schedules play an important role in adolescents’ engagement in risky behaviour, especially for boys. Non-standard parental work schedules (i.e. work during evenings, nights, weekends and rotating shifts) are positively related to fighting, drinking and trying drugs among boys and fighting among girls. In the third essay, I investigate relationships between symptoms of hyperactivity-inattention and being read to for a sample of children aged 2 to 4. The main finding, based on family fixed effects estimates, is that children who have higher hyperactivity-inattention are read to less. However, results from interactions suggest that this relationship is only present when the person most knowledgeable of the child (usually the biological mother) has less than a post-secondary degree or diploma.

The objective of this research was to investigate the behavioural, physiological and immunological effects of routine surgical procedures in neonatal swine in order to provide producers with science-based recommendations. In the first experiment, low- or average-birth-weight piglets that were tail docked and ear notched at 1 or 3 days of age showed subtle differences resulting from age at processing. However, low-birth-weight male piglets had the lowest attendance during nursing bouts and spent the greatest amount of time lying alone. Vocalization data suggests that ABW piglets may be less reactive to the procedures on d 1. Overall, the decreased vitality and reduced survivability of low-birth-weight piglets suggests that delaying processing until day 3 for these piglets may be preferable. In the second experiment, the effects of docked tail length and nursery stocking density on tail-biting behaviour, skin lesions and rectal prolapses were investigated. Long-tailed pigs (docked to 4.5 cm at birth) were most vulnerable to tail-biting, and housing at a moderate versus high nursery stocking density was not sufficient to reduce tail-biting. High nursery stocking density negatively impacted skin lesion scoring and growth performance for the majority of the grower-finisher period. Pigs from either nursery stocking density and docked tail length groups were equally likely to be affected by prolapsed rectal mucosa. Given the decreased survivability and significantly lighter weaning weight for low-birth-weight piglets compared to those of average-birth-weight, delaying processing of low-birth-weight piglets may be the most humane option. Further, until tail-biting is better understood and a more effective solution found, the routine docking of tails remains the optimal method for balancing a situation with enormous welfare-reducing potential. / Agriculture and Agri-Food Canada