Recommender systems typically work over sparse matrices. Although most methods assume so, these matrices' entries are often not missing at random (NMAR). How problematic is this? We present a puzzle. Some methods explicitly account for NMAR processes. This has been shown to improve predictions....

Conceptual models are fundamental to system analysis and design. However, the actual usage of conceptual models remains poorly understood, in particular, how and why practitioners would use multiple models in combination when doing their work. In this paper, the authors explore the reported use...

Registration of births, recording deaths by age, sex and cause, and calculating mortality levels and differentials are fundamental to evidence-based health policy, monitoring and evaluation. Yet few of the countries with the greatest need for these data have functioning systems to produce them...

Viele Investitionen in IT-Projekte – insbesondere IT-Infrastrukturinvestitionen – lassen sich inUnternehmen nur dadurch ökonomisch rechtfertigen, dass sie notwendige Voraussetzung fürdie Durchführung ertragsversprechender Folgeprojekte sind. Solche intertemporalen Abhängigkeitenzwischen...