The theoretical value of an option is evaluated according to any of several mathematical models. These models, which are developed by quantitative analysts, attempt to predict how the value of an option changes in response to changing conditions. For example how the price changes with respect to changes in time to expiration or how an increase in volatility would have an impact on the value. Hence, the risks associated with granting, owning, or trading options may be quantified and managed with a greater degree of precision, perhaps, than with some other investments. Exchange-traded options form an important class of options which have standardized contract features and trade on public exchanges, facilitating trading among independent parties. Over-the-counter options are traded between private parties, often well-capitalized institutions that have negotiated separate trading and clearing arrangements with each other.