The material in this chapter originally appeared in The UMAP Journal, 25 (4), (2004) 357-374.
Here's a quick note on attrition: Its effects can be insidious. Assume, for example, that you have 20 people in your group, and four of them quit. You have suffered 20 percent attrition. To get back to your starting point, you have to hire four people. However, that corresponds to a growth rate of 25 percent, because you have to add four to an existing team of 16. When thinking about attrition, it is important to remember that the growth factor G that you are going to have to use in computing new overall productivity is always higher than the attrition rate, because of this effect.