“Many energy companies will use models to value assets with lifetimes of 20 years or longer—things like power plants, pipelines, and natural gas wells. Even if the model was sufficient when first developed, it can still fail before its lifetime is up. Assumptions made 15 years earlier are often invalidated due to regulatory changes, population shifts, and technological changes. Exacerbating this problem is the problem of employee turnover—commonly, the original developers of the models have moved to other jobs when problems develop. After a number of years, organizations need to take steps to ensure that someone still understands every model that is in production.”