(3.3.8) Trickey : Regarding validation construed broadly: what constitutes a meaningful, hence valid, improvement in a DFA? If a DFA improves over another by 0.2 kcal/mol mean absolute error (MAE) on atomization energies and 0.02 Å on bond lengths, etc., is that really an improvement or is it in the noise of the data sets themselves? If my group produces a DFA that gives essentially the same errors on a large collection of canonical data sets as the best older DFA on the same Perdew-Schmidt rung, 339 but the new DFA is much more stable numerically or 20% faster, wouldn't such improvements be validation themselves?