Old Model, New Problem: When Should You Update a Model and What Happens When You Do?

A "quick" phone call generates a good idea, which at first blush seems a simple thing to do – apply an existing model to a new problem and then write it up. But the question "What do we have to do?" is a good one, and at second blush things are not so simple. In this short piece we talk about some of the considerations involved in applying an existing model to a new problem, in particular in deciding whether to update or not, and some of the issues involved in interpreting the output from the new application.