Offline Evaluation of Reward-Optimizing Recommender Systems: The Case of Simulation

Both in academic and industry-based research, online evaluation methods are seen as the golden standard for interactive applications like recommendation systems. Naturally, the reason for this is that we can directly measure utility metrics that rely on interventions, being the recommendations that are being shown to users. Nevertheless, online evaluation methods are costly for a number of reasons, and a clear need remains for reliable offline evaluation procedures. In industry, offline metrics are often used as a first-line evaluation to generate promising candidate models to evaluate online. In academic work, limited access to online systems makes offline metrics the de facto approach to validating novel methods. Two classes of offline metrics exist: proxy-based methods, and counterfactual methods. The first class is often poorly correlated with the online metrics we care about, and the latter class only provides theoretical guarantees under assumptions that cannot be fulfilled in real-world environments. Here, we make the case that simulation-based comparisons provide ways forward beyond offline metrics, and argue that they are a preferable means of evaluation.Comment: Accepted at the ACM RecSys 2021 Workshop on Simulation Methods for Recommender System

S100A1: A Multifaceted Therapeutic Target in Cardiovascular Disease

Cardiovascular disease is the leading cause of death worldwide, showing a dramatically growing prevalence. It is still associated with a poor clinical prognosis, indicating insufficient long-term treatment success of currently available therapeutic strategies. Investigations of the pathomechanisms underlying cardiovascular disorders uncovered the Ca2+ binding protein S100A1 as a critical regulator of both cardiac performance and vascular biology. In cardiomyocytes, S100A1 was found to interact with both the sarcoplasmic reticulum ATPase (SERCA2a) and the ryanodine receptor 2 (RyR2), resulting in substantially improved Ca2+ handling and contractile performance. Additionally, S100A1 has been described to target the cardiac sarcomere and mitochondria, leading to reduced pre-contractile passive tension as well as enhanced oxidative energy generation. In endothelial cells, molecular analyses revealed a stimulatory effect of S100A1 on endothelial NO production by increasing endothelial nitric oxide synthase activity. Emphasizing the pathophysiological relevance of S100A1, myocardial infarction in S100A1 knockout mice resulted in accelerated transition towards heart failure and excessive mortality in comparison with wild-type controls. Mice lacking S100A1 furthermore displayed significantly elevated blood pressure values with abrogated responsiveness to bradykinin. On the other hand, numerous studies in small and large animal heart failure models showed that S100A1 overexpression results in reversed maladaptive myocardial remodeling, long-term rescue of contractile performance, and superior survival in response to myocardial infarction, indicating the potential of S100A1-based therapeutic interventions. In summary, elaborate basic and translational research established S100A1 as a multifaceted therapeutic target in cardiovascular disease, providing a promising novel therapeutic strategy to future cardiologists

"We Own the Night:" Amadou Diallo's Deadly Encounter with New York City's Street Crimes Unit

Amadou Diallo died in a hail of police bullets in February 1999. The police thought Diallo was a serial rapist who was drawing a pistol against them, but Diallo was an innocent man who was unarmed. The incident has sparked a heated debate over the crime-fighting policies of Mayor Rudolph Giuliani and the New York City Police Department. To understand what has been happening in New York City in recent years, one must examine the relationship between a police officer's authority to search suspects and the legal doctrine of false imprisonment. The legal shield of false imprisonment has been sharply curtailed in recent years by Supreme Court rulings that have expanded the circumstances under which police officers can "stop and frisk" persons. In 1994 Mayor Giuliani and Police Commissioner William Bratton ordered their elite Street Crimes Unit to start confiscating illegal weapons from pedestrians. The plainclothes outfit embarked upon an aggressive campaign of stopping and frisking city residents, often illegally. Wealthy and middle-class residents were not affected by the crackdown because the police chose to exercise their search powers in the poorer neighborhoods where the crime rates were higher. Minorities bore the brunt of the crackdown, and their cries of police harassment were largely written off. The killing of Amadou Diallo was neither an act of racist violence nor some fluke accident. It was the worst-case scenario of a dangerous and reckless style of policing. Policymakers should dispense with confrontational stop-and-frisk tactics before more innocent people are injured or killed