Three observations of the economic production quantity model with imperfect quality items with/without inspection are presented in this report.
Salameh and Jaber (2000) and Maddah and Jaber (2008) models do not meet their
expected objective functions. The first observation tries to clarify the relationships among their expected objective functions and the actual ones through the derivation, the numerical simulation and statistical comparison. This report concludes s that both models are not very accurate, but capable.
Khan et al. (2011) and Khan et al. (2014) ignored the independent condition of properties of the expectation of random variables, which resulted in minor errors in both papers. The second and the third observations are the corrections of the models of two papers, respectively. Numerical comparisons show the differences between the original models and the revisions are minor, but significant. An example of a multi-factor sensitivity analysis is shown in this report.