On the first page (page 28) in the third column they make the statement that:
Models of complex systems, especially those that incorporate human behavior, such as that demonstrated in combat, do not often lend themselves to empirical validation of output measures, such as attrition.
Really? Why can’t you? If fact, isn’t that exactly the model you should be validating?
More to the point, people have validated attrition models. Let me list a few cases (this list is not exhaustive):
1. Done by Center for Army Analysis (CAA) for the CEM (Concepts Evaluation Model) using Ardennes Campaign Simulation Study (ARCAS) data. Take a look at this study done for Stochastic CEM (STOCEM): https://apps.dtic.mil/dtic/tr/fulltext/u2/a489349.pdf
2. Done in 2005 by The Dupuy Institute for six different casualty estimation methodologies as part of Casualty Estimation Methodologies Studies. This was work done for the Army Medical Department and funded by DUSA (OR). It is listed here as report CE-1: http://www.dupuyinstitute.org/tdipub3.htm
3. Done in 2006 by The Dupuy Institute for the TNDM (Tactical Numerical Deterministic Model) using Corps and Division-level data. This effort was funded by Boeing, not the U.S. government. This is discussed in depth in Chapter 19 of my book War by Numbers (pages 299-324) where we show 20 charts from such an effort. Let me show you one from page 315:
So, this is something that multiple people have done on multiple occasions. It is not so difficult that The Dupuy Institute was not able to do it. TRADOC is an organization with around 38,000 military and civilian employees, plus who knows how many contractors. I think this is something they could also do if they had the desire.