A note on impact of investing in quality improvement on the lot size model

Recently Keller and Noori studied a model for investing in quality improvement on the lot size model. They extended Porteus’ work to the case where demand during the lead time is probabilistic. They obtained explicit solutions for two specific demand distributions using a logarithmic investment function. However, it can be shown that there is a mistake in their solution procedure, and consequently, there is a need for some properties of the cost function and the optimal solution similar to those in Porteus.