The weighted jackknife for ratio estimation

Using the idea of impirical influence function, Hinkley (1977), the weighted jackknife technique is extended to ratio estimation. A weighted jackknife variance estimator for the ratio estimator is developed. Using the prediction theory approach, the properties of the weighted jackknifed variance estimator are examined. The implications of the failures of regression model on the behaviour of the weighted jackknifed variance estimator, for ratio estimation, are also studied.     

Assessing Overweight,Obesity, Diet,and Physical Activity in College Students

Abstract

The authors surveyed 738 college students aged 18 to 27 years to assess overweight, obesity, dietary habits, and physical activity. They used BMI (body mass index) > 25 kg/m² or BMI > 85th percentile and BMI > 30 kg/m¹ or BMI > 95th percentile to estimate overweight and obesity in those aged < 19 years. To define overweight and obesity in those > 20 years, they used BMI > 25 kg/m² and > 30 kg/m². They found overweight rates of 21.6% using BMI directly and 16.2% using BMI percentile and obesity rates of 4.9% using BMI directly and 4.2% using BMI percentile. More than 69% of the participants reported < 5 servings of fruits and vegetables per day and more than 67% reported < 20 g of fiber per day; participants reported physical activity on fewer than 3 d/wk. Most college students are not meeting dietary and physical activity guidelines, suggesting the need for prevention interventions and increased understanding of overweight in college students.     

Assessing overweight, obesity, diet, and physical activity in college students

The authors surveyed 738 college students aged 18 to 27 years to assess overweight, obesity, dietary habits, and physical activity. They used BMI (body mass index) > or = 25 kg/m2 or BMI > or = 85th percentile and BMI > or = 30 kg/m2 or BMI > or = 95th percentile to estimate overweight and obesity in those aged < or = 19 years. To define overweight and obesity in those > or = 20 years, they used BMI > or = 25 kg/m2 and > or = 30 kg/m2. They found overweight rates of 21.6% using BMI directly and 16.2% using BMI percentile and obesity rates of 4.9% using BMI directly and 4.2% using BMI percentile. More than 69% of the participants reported < 5 servings of fruits and vegetables per day and more than 67% reported < 20 g of fiber per day; participants reported physical activity on fewer than 3 d/wk. Most college students are not meeting dietary and physical activity guidelines, suggesting the need for prevention interventions and increased understanding of overweight in college students.     

Clearing the air: American Indian tribal college students' exposure to second hand smoke & attitudes towards smoke free campus policies

Objective: The purpose of this study was to examine knowledge, awareness, and support for campus smoke-free policies. Participants: 1,256 American Indian tribal college students from three tribal colleges in the Midwest and Northern Plains. Methods: Data are from an observational cross-sectional study of American Indian tribal college students, collected through a web-based survey. Results: Only 40% of tribal college students reported not being exposed to second hand smoke in the past 7 days. A majority of nonsmokers (66%) agreed or strongly agreed with having a smoke-free campus, while 34.2% of smokers also agreed or strongly agreed. Overall, more than a third (36.6%) of tribal college students were not aware of their campus smoking policies. Conclusions: Tribal campuses serving American Indian students have been much slower in adopting smoke-free campus policies. Our findings show that tribal college students would support a smoke-free campus policy.     

Healthcare providers' treatment of college smokers

About 28% of college students smoke tobacco, and many will continue smoking into adulthood. Although little is known about how to help college students quit smoking, 1 promising strategy is healthcare providers' advice. To estimate their life-time receipt of brief advice and to identify characteristics that predict who may receive that advice, 348 college students completed a survey about their smoking and related practices. Seventy-seven percent of the smokers (73% of the students) were asked about smoking. Of those smokers, 57% were advised to quit, 22% were given advice about quitting, 5% were helped with setting a quit date, and 4% were offered follow-up. Occasional smokers were less likely than daily smokers to be advised to quit. Although 36.2% of the smokers did not report their smoking accurately, smokers who were accurate were more likely to be advised to quit and to be given advice about quitting.     

Subsea Release of Oil from a Riser: An Ecological Risk Assessment

This study illustrates a newly developed methodology, as a part of the U.S. EPA ecological risk assessment (ERA) framework, to predict exposure concentrations in a marine environment due to underwater release of oil and gas. It combines the hydrodynamics of underwater blowout, weathering algorithms, and multimedia fate and transport to measure the exposure concentration. Naphthalene and methane are used as surrogate compounds for oil and gas, respectively. Uncertainties are accounted for in multimedia input parameters in the analysis. The 95th percentile of the exposure concentration (EC_95%) is taken as the representative exposure concentration for the risk estimation. A bootstrapping method is utilized to characterize EC_95% and associated uncertainty. The toxicity data of 19 species available in the literature are used to calculate the 5th percentile of the predicted no observed effect concentration (PNEC_5%) by employing the bootstrapping method. The risk is characterized by transforming the risk quotient (RQ), which is the ratio of EC_95% to PNEC_5%, into a cumulative risk distribution. This article describes a probabilistic basis for the ERA, which is essential from risk management and decision‐making viewpoints. Two case studies of underwater oil and gas mixture release, and oil release with no gaseous mixture are used to show the systematic implementation of the methodology, elements of ERA, and the probabilistic method in assessing and characterizing the risk.     

Characteristics of social smoking among college students

Social smoking is a newly identified phenomenon in the young adult population that is poorly understood. We investigated differences in social smoking (smoking most commonly while partying or socializing) and other smoking within a convenience sample of college smokers (n = 351) from a large midwestern university. Results revealed that 70% of 351 current (past 30-day) smokers reported social smoking. No significant difference was found in motivation to quit between smoking groups. However, a significant difference was found between groups in confidence to quit, the number of days smoked, and the number of cigarettes smoked on those days. More social smokers than expected did not perceive themselves as smokers. Logistic regression analysis revealed that lower physical and psychological dependence and higher social support scores predicted social smoking.