Assessing and Improving the Performance of Nearly Efficient Unit Root Tests in Small Samples

Abstract

The development of unit root tests continues unabated, with many recent contributions using techniques such as generalized least squares (GLS) detrending and recursive detrending to improve the power of the test. In this article, the relation between the seemingly disparate tests is demonstrated by algebraically nesting all of them as ratios of quadratic forms in normal variables. By doing so, and using the exact sampling distribution of the ratio, it is straightforward to compute, examine, and compare the test' critical values and power functions. It is shown that use of GLS detrending parameters other than those recommended in the literature can lead to substantial power improvements. The open and important question regarding the nature of the first observation is addressed. Tests with high power are proposed irrespective of the distribution of the initial observation, which should be of great use in practical applications.     

Structural holes and managerial performance: Identifying the underlying mechanisms

Structural holes theory suggests a variety of possible explanations for the empirically observed relationship between structural holes and individual managerial performance. However, little has been done to disentangle one mechanism from another. This paper empirically tests a mediated moderation model that distinguishes between the five different theoretical mechanisms: autonomy, competition, information brokering, opportunity recognition and innovativeness. The findings suggest that of these five theoretical causal motors, innovativeness plays a key role in linking network structure and network content to performance.     

Examining the structure of awareness and perceptions of groundnut aflatoxin among Ghanaian health and agricultural professionals and its influence on their actions

This study uses a modified health belief model (HBM) within a socio-economic framework to evaluate the influence of awareness and knowledge on actions to reduce aflatoxin (AF) contamination in groundnuts (peanuts). Data were collected in 2002 through a self-administered questionnaire from a sample of 367 individuals. Socio-economic factors affecting perceptions, awareness, knowledge, and action were examined using structural equation modeling. The perceived benefits of good quality groundnuts and/or groundnut products were the most important determinants of awareness and knowledge of AF among agricultural and health professionals in Ghana. Awareness, in turn, had a significant causal effect on the professionals’ decisions to take actions to increase the level of awareness of AF in the society. Demographic factors, such as gender and level of education significantly influenced knowledge of AF and the perception of the benefits of good quality groundnut. Type of profession had a significant influence on awareness and perceived seriousness of the AF problem. Education was a significant determinant of awareness of AF in groundnuts. The study generates important information for policy decision making when considering resource allocation to reduce food contamination in developing economies.     

When the Learning Disabled Go to College

Abstract

During the last decade, federal laws have provided for remedial education in elementary and secondary schools for students with learning disabilities, preparing large numbers of them for college. Federal law also mandates helping learning-disabled students with their needs once they matriculate. Declining numbers of high school graduates in the aftermath of the baby boom have made more colleges open their doors to these students. The disabilities, and the accommodations they require, arrive in college with the rest of a student's baggage, demanding attention. Colleges and universities have chosen a variety of approaches, from specific remedial programs and individual accomodations according to need to more general programs. Some colleges pretend these disabilities do not exist and seem oblivious to their presence on campus. Learning disabilities can have an impact in every class and lecture hall and can contribute to unhappiness and the college's attrition rate. On the other hand, responsive and responsible programs provide students with the resources for the same education, honors, and opportunities as their nondisabled peers.     

Suicide ideation among US college students. Associations with other injury risk behaviors

Suicide, the endpoint of a continuum that begins with suicide ideation, is the third leading cause of death among the US college-aged population. The first and second leading causes of death among this age group, unintentional injury and homicide, may also be linked to suicide ideation. We used data from the National College Health Risk Behavior Survey to examine the association between suicide ideation and injury-related behaviors among 18- to 24-year-old college students. Students who reported suicide ideation were significantly more likely than students who did not report considering suicide to carry a weapon, engage in a physical fight, boat or swim after drinking alcohol, ride with a driver who had been drinking alcohol, drive after drinking alcohol, and rarely or never used seat belts. Given this clustering of injury-related risk behaviors, college prevention programs should aim to reduce risks for injuries comprehensively, rather than addressing each risk behavior separately.     

A comparative assessment of public opinion toward immigrants and immigration policies

"This article is part of a larger study of public attitudes toward immigration in seven countries that historically and currently have had different policies and practices vis-a-vis immigration. The countries involved are Australia, Canada, France, Germany, Great Britain, Japan and the United States. The time frame for which most of the public opinion data will be reported is from 1970 through 1995. The data have been collected from national surveys that were conducted in each of the countries."     

Revisiting the relationships among gender,marital status,and mental health

Three decades ago, Grove introduced his sex-role theory of mental illness, which attributes women's higher rates of psychological distress to their roles in society. Central to his hypothesis is that marriage is emotionally advantageous for men and disadvantageous for women. This article revisits this topic with data from the National Survey of Families and Households. The analyses indicate that the emotional benefits of marriage apply equally to men and women, but that men and women respond to marital transitions with different types of emotional problems. The implications of these findings for future research on gender and mental health are discussed.