# Production and Maintenance Planning for a Deteriorating System with Operation-Dependent Defectives
## 7 Comparative Study  
The objective of this section is to compare the obtained joint control policy in order to illustrate the advantage of applying our approach in practice and highlight the economic benefit that decision-makers can obtain at implementing our joint strategy. We should note that the joint production and maintenance policies proposed in this paper have not been studied under the same assumptions of deterioration and operation-dependent defectives in the literature yet. However, we have managed to compare the total cost incurred from our joint control policy with the total cost reported from other policies based on assumptions common in the literature that does not takes into account the effects of deterioration on the control parameters. The policies considered in the comparison are described as follows:  
* Policy-I: defines the production scenario (basic case) of the joint control policy obtained in Section 5, where the production and maintenance policies are determined simultaneously in an integrated model. The particularity of Policy-I is that the production threshold is dynamic, it is adjusted progressively in function of the level of deterioration of the machine, and major maintenance can be once the machine has reached a certain level of deterioration that justifies the cost of such type of maintenance. Thus, the conduction of major maintenance has a feedback on the level of deterioration of the machine. * Policy-II: this policy is derived from the previous policy with the difference that the production threshold is not adjusted progressively, it remains constant at a given level for all the considered time interval and it does not evolve in function of the deterioration of the machine. Nevertheless, the conduction of major maintenance can be conducted based on a feedback with the deterioration of the machine as in Policy-I. * Policy-III: the production threshold is dynamic and it is adjusted in function of the deterioration of the machine as in Policy I. However, major maintenance is conducted only when the machine has reached its maximum age limit. Table 3 summarizes the different production scenarios considered in the comparison, it presents the total cost incurred when the level of deterioration of the system recommends the performance of a major maintenance and also such table presents the observed differences in the total cost. The results presented in Table 3, were obtained with the same data parameters shown in Tables 1 and 2. The interpretation of the obtained results of Table 3 implies that Policy-II reported a cost 17.79% higher than our joint control Policy-I, because Policy-II fails to consider the strong effect of the deterioration process on the production control rule. Maintaining a constant production threshold is not profitable in Policy-II, because it is evident that as the machine deteriorates it produces more defectives and also it is subject to more frequent failures. Thus, the production threshold must be progressively increased as a countermeasure to avoid shortages and ensure demand satisfaction with flawless units, as in Policy-I. \begin{table}
\begin{tabular}{c c c c c} \hline
**Scenario** & **Production Threshold \(Z\)** & **Major Maintenance \(w\)** & **Optimal Total Cost** & **Cost Difference \(\Delta\) (\%)** \\ \hline Policy-I (basic case) & dynamic & feedback with deterioration & 83.16 & - \\ Policy-II & constant & feedback with deterioration & 97.96 & 17.79\% \\ Policy-III & dynamic & conducted at the age limit & 113.40 & 36.36\% \\ \hline \end{tabular}
\end{table} 
Table 3: Cost difference of the comparative study. With respect to the total cost obtained by Policy-III, we noted that it reported a cost 36.36% more expensive than the cost of Policy-I. The observed cost difference is given mainly because the production and maintenance strategies in Policy-III are not determined simultaneously.