學術論文

警方包庇有組織犯罪的情況偶有所聞，但往往很難通過實證來研究。研究利用來自中國獨特的性交易數據，證實地方警察或對一些有組織的賣淫活動提供庇護。具體而言，位於警力密度較高的社區內的桑拿浴室和按摩院，受到警方「保護」的機會較高，進而可以進行高風險、高罪責的賣淫活動。在地方警察「掃黃」期間，這種庇護效應更加明顯，意味著選擇性執法的存在。地方領導層的變化和中央政府紀律部隊巡視則會顯著減弱這種庇護效應。

電動車充電站的地點是否便利，是電動車普及的一項重要因素而電動車的普及是一項有效減少碳排放量的綠色科技。有見及此，不少地方政府都想方設法，達到電動車普及化的目標，例如直資興建額外的電動車充電站或以資助方式吸引汽車製造商興建更多電動車充電站。為此，政府需與汽車製造商協調，以確保充電站的數量達到最佳的規劃。透過研究政府、汽車製造商及消費者的互動，我們總結三方互動過程中所產生的協調問題。平衡分析得出三個主要結論：第一，在各方獨立承擔建築成本的情況下，政府及汽車製造商均應興建額外的電動車充電站。而且，只有當興建電動車充電站的目標數量及建築成本都處於高水平時，政府才應向汽車製造商就興建每個充電站提供資助。然而，若汽車製造商的建築成本取決於政府興建電動車充電站的數量，那麼政府便應委派汽車製造商興建充電站，並就興建每個興建的充電站提供資助。第二，若政府向消費者購買電動車提供額外補助，研究顯示這額外補助措施較向汽車製造商就興建每個充電站提供資助更具成本效益。第三，不論政府的目標是改善電動車普及度或消費者福利，最理想的政策的結構是一樣的。此項研究結果可供政府與汽車製造商協調興建電動車充電站時作參考，以進一步改善電動車普及度和加強消費者福利。

Emergency department (ED) overcrowding and long patient wait times have become a worldwide problem. We propose a novel approach to assigning physicians to shifts such that ED wait times are reduced without adding new physicians. In particular, we extend the physician rostering problem by including heterogeneity among emergency physicians in terms of their productivity (measured by the number of new patients seen in 1 hour) and by considering the stochastic nature of patient arrivals and physician productivity. We formulate the physician rostering problem as a two-stage stochastic program and solve it with a sample average approximation and the L-shaped method. To formulate the problem, we investigate the major drivers of physician productivity using patient visit data from our partner ED, and find that the individual physician, shift hour, and shift type (e.g., day or night) are the determining factors of ED productivity. A simulation study calibrated using real data shows that the new scheduling method can reduce patient wait times by as much as 13% compared to the current scheduling system at our study ED. We also demonstrate how to incorporate physician preference in scheduling through physician clustering based on productivity. Our simulation results show that EDs can receive almost the full benefit of the new scheduling method even when the number of clusters is small.

For a queueing system with multiple customer types differing in service-time distributions and waiting costs, it is well known that the cµ-rule is optimal if costs for waiting are incurred linearly with time. In this paper, we seek to identify policies that minimize the long-run average cost under nonlinear waiting cost functions within the set of fixed priority policies that only use the type identities of customers independently of the system state. For a single-server queueing system with Poisson arrivals and two or more customer types, we first show that some form of the cµ-rule holds with the caveat that the indices are complex, depending on the arrival rate, higher moments of service time, and proportions of customer types. Under quadratic cost functions, we provide a set of conditions that determine whether to give priority to one type over the other or not to give priority but serve them according to first-come, first-served (FCFS). These conditions lead to useful insights into when strict (and fixed) priority policies should be preferred over FCFS and when they should be avoided. For example, we find that, when traffic is heavy, service times are highly variable, and the customer types are not heterogenous, so then prioritizing one type over the other (especially a proportionally dominant type) would be worse than not assigning any priority. By means of a numerical study, we generate further insights into more specific conditions under which fixed priority policies can be considered as an alternative to FCFS.

Using China's 2008 four-trillion-yuan economic stimulus as a setting and proprietary loan data, we study how a large publicly listed state-owned bank responds to the government's countercyclical financing initiative while trying to meet the expectations of bank regulators and public investors. We find that the bank exhibited little changes in the process of setting internal credit ratings of borrowers, and internal ratings remain a valid, albeit weaker, predictor of interest rates in the stimulus period. Interest rates also remain a valid predictor of loan delinquency in the stimulus period. Evidence from analyzing unlisted borrowers is broadly similar. Overall, there is no systematic evidence that loan decisions of the state-owned bank are severely compromised in the stimulus period. The study adds to the limited understanding of how partially privatized state-owned banks balance different objectives in managing credit risk and is relevant to the longstanding debate over the roles of state-owned banks.

社會信任能夠減輕契約不完備性，因而會對委託投資組合管理的活躍度和成效有重要的影響。我們利用一個環球開放互惠基金的完整樣本進行研究，發現社會信任度與基金的活躍度屬正相關關係，而由此帶來主動投資表現卓越（例如：每年產生約2%的收益）。此外，「信任市場」和「信任投資經理」兩者在不同類型的跨境委託投資組合管理方面，發揮著重要但不同的作用。總體而言，該研究結果證明信任度是委託投資組合管理的重要基石。

研究利用中國引入高速鐵路 (HSR) 的項目作為獲取訊息成本的外來衝擊因素，發現獲取訊息成本降低可導致 (i) 訊息生產量顯著增加 (從分析師更頻密地到訪投資組合公司足可證明)，以及 (ii) 生產質量有所提升 (從分析師能夠提高預測準確度及提出更好的投資建議中展現)。對於難以生產訊息的公司，以上的影響尤其明顯。重要的是，訊息生產量提升與改善價格效益有所關聯。通過對財務分析師進行大規模統計調查，我們進一步證實了上述的發現。最後，實證和調查結果都指出軟訊息對分析師建立獨特訊息十分重要。

研究透過薪資保護計劃向上市公司提供貸款的數據，區分銀行和公司因人際關係而造成偏袒和信息優勢這兩個因素。由於薪資保護計劃的貸款由政府作擔保，因此銀行毋需對貸款人進行嚴格的審查，這有效減少信息摩擦，並可量化偏袒行為的效應。研究發現與銀行有私人聯繫的公司，較容易獲取薪資保護計劃的貸款。當公司的財務越透明，此等私人聯繫的作用會因而減弱，但並不會因銀行的企業管治而產生變化。研究亦指出，為避免監管審查，關聯公司還款機率較大。整體而言，我們就銀行借貸的偏袒行為提出清晰的估算，並突顯政府計劃利用銀行體系分配資本時，所帶來意想不到的後果。

中國在不同縣市實施的最低工資政策有所不同。此研究透過使用中國製造業企業的工業普查數據，探討最低工資政策如何影響資本投資。利用最低工資政策在縣市邊界的不連續性，我們發現最低工資政策會增加資本投資。企業的勞動密集度越高，技術提升空間越大，以及企業無法將勞動成本轉嫁予消費者時，其對於最低工資政策所作出的投資反應越大。研究中一項基於縣市管轄權變化的自然實驗進一步確定了最低工資與資本投資的因果關係。