The foundations of modern risk measurement rest on a framework that uses past returns to measure or estimate the distribution of future returns. The stability of the recent past, even if much of it proves durable, probably understates potential risk. The parameters used to estimate value at risk can produce very large differences in predicted exposure, especially at extreme confidence intervals.
Estimating the potential interactions among these exposures in conditions of stress is even harder, due to the uncertainty about the behavior of investors and other market participants and because of the potential effects of financial distress on overall economic activity.
The relatively short history of returns for new products, the complexity of measuring exposure in many new instruments and limitations on transparency also create the potential for classic “agency” problems—internal conflicts of interest that can lead to problematic outcomes.