Optimal number of accrual groups and accrual group sizes in longitudinal trials with discrete‐time survival endpoints

In longitudinal trials, the number of accrual groups and their sizes should carefully be chosen to ensure a desired power to detect a specified treatment effect. Methods are proposed to obtain a cost‐effective combination of the number and size of accrual groups that provides high efficiency at minimal cost. We focus on trials where an event occurs at any point in time, but it is recorded on a discrete scale. The Weibull survival function is considered for modeling the underlying time to event. By using a cost function, it is shown that the ratio of the cost of recruiting and treating subjects to the cost of measuring them and also the survival pattern highly influence the optimal combination of the number and size of accrual groups. A maximin approach is further presented to obtain robust designs with respect to poor specification of these modeling parameters. We also show the application of the proposed optimal design methodology using real examples.     

Market Moods and Network Dynamics of Stock Returns: The Bipolar Behavior

The authors show that a simple mood-separable preference in a network study of stock returns captures a variety of stylized facts regarding stocks’ provisional (ab)normal behavior. These behaviors are articulated in a multistate complete Euclidean network model that specifies the existence, direction, and magnitude of a self-organized dynamics for each individual stock during abnormal market moods. In the empirical setting, the authors apply suggested model along with 2 established visual approaches (multidimensional scaling and agglomerative hierarchical clustering) for benchmark purposes. Results reveal different levels of erratic return dynamics for each stock and the entire market in different abnormal market moods. The authors model and interpret these self-organized dynamics as evidence of stocks’ and market’s bipolar behavior.     

Reputation and adverse selection: theory and evidence from eBay

How can a marketplace introduce mechanisms to overcome inefficiencies caused by adverse selection? In this article, I use a unique data set that follows eBay sellers to show that reputation is a major determinant of price variations. I develop a model of sellers' dynamic behavior where sellers have heterogeneous qualities unobservable by buyers. Using reputation as a signal of quality, I structurally estimate the model to uncover buyers' utility and sellers' costs and underlying qualities. I show that removing the reputation mechanism increases low‐quality sellers' market share, lowers prices, and consequently reduces sellers' profit by 66% and consumer surplus by 35%.     

Revisiting sacrifice and stigma: Why older churches become more liberal

This paper revisits the concept of ‘Sacrifice and Stigma’ first introduced in the seminal model of Iannaccone, published in 1992. Iannaccone provides an explanation for the rise of strict churches in face of the decline of liberal ones. He argues that costly and stigmatizing requirements, which make a church distinctive and strict, reduce free-riding in the group, conferring it a competitive edge. His model, however, does not address the question of why certain churches, generally older and larger, become more liberal and easygoing. I argue that for established groups, which rely on intergenerational transmission of religious preference, ‘sacrifice and stigma’ are no longer means of screening free-riders but determine the depreciation rate of the stock of religious capital of the group. Modeling the setting as a differential game, I show that in such circumstances, a reduction in the required ‘sacrifice and stigma’ increases the steady-state level of contribution to the church.     

Reservations on the use of event studies to evaluate economic policy

Event studies represent an increasingly popular method to evaluate the welfare effects of economic policy decisions. The basic idea is that stock market reactions to the announcement of policy decisions contain superior information about the welfare effects of these decisions. This paper investigates the degree of reliability of event studies as a policy evaluation method by critically reflecting upon two underlying assumptions. Since both the information superiority of financial markets and the determination of economic welfare effects based on abnormal returns consist of considerable interpretation problems, we issue a note of caution: scientists and policy makers should be very reluctant to rely on stock market reactions as a referee on economic policy decisions. Event studies cannot replace thorough theoretical economic analysis.     

The role of wasta in repatriates’ perceptions of a breach to the psychological contract: a Saudi Arabian case study

This study examines the influence of a national cultural dimension, specifically a strong orientation towards collectivism/reliance on network relationships, referred to as ‘wasta’, on the way in which psychological contracts form and change in a Saudi organisation. Specifically, it focuses upon how the psychological contract is perceived to have been breached by repatriates because of the role that wasta plays in shaping formal and informal HR practices pre- and post-assignment. The analysis demonstrates that prior to international assignment, wasta was taken for granted and only implicitly acknowledged as influencing selection criteria for assignments and individuals’ expectations and obligations associated with their psychological contract. Once repatriated, wasta was foregrounded and perceived as highly problematic in terms of career advancement. This shaped repatriates’ perceptions that their psychological contract had been breached, influencing their intentions to leave. These findings suggest that the psychological contract can be viewed as highly context-specific, as well as a person-centred phenomenon. We consider the implications of our research in terms of the influence of national cultural characteristics on individual’s perceptions of breaches to the psychological contract and highlight the possible implications generally for Saudi Arabia, which is aiming to be less reliant on foreign labour.     

Life-course and entry to entrepreneurship:embedded in gender and gender-egalitarianism

ABSTRACT

Prior research has suggested that low gender egalitarianism results in a gender gap in entrepreneurship participation, as it provides men and women with different opportunities and constraints. However, this research has primarily relied on an unrealistic assumption, namely that gender-related opportunities and constraints occur evenly throughout different life stages. This paper details an institutional life-course model that explains gender-related patterns in individuals’ propensity to enter entrepreneurship and contingencies related to the level of gender-egalitarianism in society and individuals’ life stages. We test our conceptual model on a unique integrated dataset from the Global Entrepreneurship Monitor and the World Value Survey, encompassing a total of 672,781 adults in 71 countries.     

Dimensions of self-selected leisure activities,trait coping and their relationships with sleep quality and depressive symptoms

Although leisure is presumed to be beneficial, certain profiles of leisure may be especially good. This paper tests whether dimensions of self-selected leisure activities (SSLAs) differentially relate to depressive symptoms and poor sleep quality, including (a) positivity (SSLA-PO), (b) difficulty (SSLA-DF), (c) distraction (SSLA-DI) and (d) thinking about negative events (SSLA-TN). Furthermore, it tests whether those low in perseverative cognitions (PCs) and high in ‘John Henryism’ active coping are equally likely to benefit from leisure. Participants (n = 362, 76% female) at a large university in Wisconsin rated two SSLAs on the dimensions above and completed measures of depression, sleep quality, PCs and active coping. Regression analyses showed that SSLA-TN predicted greater depression and poor sleep quality. For the moderators, more SSLA-DI and SSLA-TN each predicted greater depression for those more prone to PCs, and more SSLA-DI predicted more depression and worse sleep quality at lower active coping levels. Results suggest that not all leisure is equally beneficial, and have implications for the design of leisure-based interventions.