TESTS FOR DETECTING MORE NBU-NESS AT A SPECIFIC AGE

This paper proposes a class of non‐parametric test procedures for testing the null hypothesis that two distributions, F and G, are equal versus the alternative hypothesis that F is ‘more NBU (new better than used) at specified age t₀’ than G. Using Hoeffding's two‐sample U‐statistic theorem, it establishes the asymptotic normality of the test statistics and produces a class of asymptotically distribution‐free tests. Pitman asymptotic efficacies of the proposed tests are calculated with respect to the location and shape parameters. A numerical example is provided for illustrative purposes.     

Imputation using response probability

The authors propose a new ratio imputation method using response probability. Their estimator can be justified either under the response model or under the imputation model; it is thus doubly protected against the failure of either of these models. The authors also propose a variance estimator that can be justified under the two models. Their methodology is applicable whether the response probabilities are estimated or known. A small simulation study illustrates their technique.     

Minimax Designs for the Stability of Slope Estimation on Second-order Response Surfaces

In this paper, designs for the stability of the slope estimation on a second-order response surface are considered. Minimization of the point dispersion measure, which is maximized over all points in the region of interest is taken as the optimality criterion, and the minimax properties in some class of designs are derived in spherical and cubic regions of interest. We study the efficiencies of the minimax designs relative to other optimal designs with various criteria.     

What drives successful social networking services? A comparative analysis of user acceptance of Facebook and Twitter

This study identifies perceived mobility, security, connectedness, system and service quality, usefulness, attitude, and flow experience as key motivational factors for using social networking services (SNSs), and develops a theoretical model that explicates the process in which users adopt Facebook and Twitter by integrating these factors with the technology acceptance model (TAM). While results of structural equation modeling (SEM) on the collected data (N = 2,214) verified the validity and reliability of the research model, Facebook and Twitter users were found to emphasize different motivational factors when deciding to use SNSs. The implications of notable findings and directions for future studies are discussed.     

Educational expansion and changes in occupational returns to education in Korea

We use data from the Korean Labor and Income Panel Study (KLIPS) conducted in 1998 by the Korean Labor Institute to examine the school-to-work transition across three labor market entry cohorts of Korean men and women. Taking into account the dramatic expansion of educational system and economic changes Korean society has experienced during the last few decades, we develop hypotheses about possible changes in the effects of educational qualifications on first occupational attainment. We first conduct an OLS regression of first occupational prestige scores on education. We then look at the effects of education on the odds of entering an occupational class using multinomial logit models. The results of the two analyses indicate that educational qualifications strongly affect occupational attainment for both men and women. The effects of education, particularly junior college and university, on first occupation have declined across three labor market cohorts for women but not for men.     

Patterns and trends of educational mating in Korea

This study examines the patterns and trends in the association between wives' and husbands' educational attainment during 1950-79 in Korea. Log-linear analysis traces the educational mating of successive marriage cohorts using Korean censuses. The most prominent feature in educational mating in Korea over time has been a rapid increase in college homogamy during 1960-79, which has increased 3 times every decade since the 1950s. This increase reflects the increasing rigidity of the status order in Korea during the 1960s and 1970s. This result is consistent with the conflict perspective which argues that the dominant strata consolidates its class culture though homogamous marriages. From 1970 to 1979 hypergamy increased in Korea, sustaining the traditional marriage pattern while Korea underwent industrialization. Although Korean couples who married during the 1970-79 period have greater educational hypogamy, it is thought to be due to demographic changes in age heterogamous couples.     

Supply Chain Design and Carbon Penalty: Monopoly vs. Monopolistic Competition

This paper studies whether imposing carbon costs changes the supply chain structure and social welfare. We explore the problem from a central policymaker's perspective who wants to maximize social welfare. We consider two stakeholders, retailers, and consumers, who optimize their own objectives (i.e., profits and net utility) and three competitive settings (i.e., monopoly, monopolistic competition with symmetric market share, and monopolistic competition with asymmetric market share). For the monopoly case, we find that when the retailer's profit is high, imposing some carbon emission charges on the retailer and the consumers does not substantially change the supply chain structure or the social welfare. However, when the retailer's profit is low, imposing carbon costs optimally can lead to a significant increase in social welfare. Moreover, the impact of imposing carbon emission charges becomes more significant when the degree of competition increases. Additionally, the quantum of benefit may depend only on factors common across industries, such as fuel and carbon costs.