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We present a new challenging stance detection dataset, called Will-They-Won't-They 1 (WT-WT), which contains 51,284 tweets in English, making it by far the largest available dataset of the type. All the annotations are carried out by experts; therefore, the dataset constitutes a high-quality and reliable benchmark for future research in stance detection. Our experiments with a wide range of recent state-of-the-art stance detection systems show that the dataset poses a strong challenge to existing models in this domain. The entire dataset is released for future research 2 .

This article studies a model of disease propagation in which rational and forward‐looking individuals can control their exposure to infection by engaging in costly preventive behavior. Equilibrium outcomes under decentralized decision making are characterized and contrasted to the outcomes chosen by a social planner. In general, individuals overexpose themselves to infection, leading to suboptimally high disease prevalence. The model is applied to study the welfare effects of preexposure prophylaxis, which reduces transmission between serodiscordant couples and causes disinhibition. It is shown that a decrease in the induced infection risks increases disease prevalence and can lead to decreases in overall welfare.

PHONE: [972]-2-6584135 FAX: [972]-2-6513681 E-MAIL: ratio@math.huji.ac.il URL: http://www.ratio.huji.ac.il/ Abstract.This paper proposes an explanation of merger waves based on the interaction between competitive pressure and irreversibility of mergers in an uncertain environment. A set of acquirers compete over time for scarce targets. At each point in time, an acquirer can either postpone a takeover attempt, or raid immediately. By postponing the takeover attempt, an acquirer may gain from more favorable future market conditions, but runs the risk of being preempted by rivals. First, a complete information model is considered, and it is shown that the above tradeoff leads to a continuum of subgame perfect equilibria in monotone strategies that are strictly Pareto ranked. All these equilibria share the feature that all acquirers rush simultaneously in merger waves. The model is then extended to a dynamic global game by introducing slightly noisy private information about merger profitability. This game is shown to have a unique Markov perfect Bayesian equilibrium in monotone strategies, and the timing of the merger wave can thus be predicted. Last, the comparative dynamics predictions of the model are related to stylized facts.