## Intelligent System to Support the Decision-Making Process in Lean Maintenance Management  
### Selection of Decision Variables in the Evaluation Process  
To assess the effectiveness of lean maintenance tools, the factors influencing the dependent variable were identified. In the research on the assessment of the effectiveness of lean maintenance tools, one dependent variable and 19 explanatory variables (predictors) were determined. In the conducted research, one dependent variable was assumed: the average value of the OEE indicator. Due to the large variety (combination) of response options, three additional indicators were introduced in the surveyed enterprises: maintenance strategy indicator (MSI), number of preventive activities (NPA), and number of TPM activities (NTPMA) indicator. The NPA number is the number of actions to prevent unplanned downtime, calculated as the total value of actions carried out simultaneously by the enterprise. During the survey (data collection) process, the company could choose several activities from the following:  
1. Implementation of autonomous service (by the operator). 2. Implementation of preventive maintenance. 3. Forecasting activities based on the condition of machines (e.g., vibration analysis). 4. Additional operator training. 5. Additional training of maintenance service employees. 6. Equipping the maintenance services with specialized instruments (e.g., for measuring vibrations, for measuring the noise level). 7. Exchange of machines for new ones. 8. Modernization of machines. 9. Increasing the number of employees of maintenance services. 10. Outsourcing some maintenance activities to external companies. Depending on how many activities are carried out by the enterprise at the same time, the indicator may range from 1 to 10. In addition, during the survey (data collection) process, the company could choose several activities implemented as part of the implementation of the TPM method, recommended in the literature on the subject, from the following:  
1. Training of selected employees. 2. Training of all employees. 3. Implementation in a selected pilot area (position, line, etc.). 4. TPM workshops in the selected pilot area (stand, line, etc.). 5. Assessment of machines in terms of meeting health and safety requirements. 6. Assessment of the technical condition of machines. 7. Identification of non-conformities on machines. 8. Development of the inspection schedule. 9. Development of a renovation schedule. 10. Development of the scope of preventive service (for maintenance services). 11. Development of the scope of autonomous service (for the operator). \[NTPMA=\ \frac{\sum_{i=1}^{11}x_{i}}{\text{max\emph{number of activities}}}*100\% \tag{3}\]Depending on the value obtained, the indicator had four levels: low, medium, high and very high (Table 3). The last index developed is the MSI index. With this indicator, it is possible to determine what technical infrastructure management strategy is applied by the enterprise. During the study (data collection), the company could choose several activities defining the realized activities implemented under the corrective maintenance (CM), preventive maintenance (PM), and condition-based maintenance (CBM) strategies. In order to define the index for possible variants of answers, numerical values ranging from 1 to 7 were introduced (Table 4). The lowest value was given to the action implemented in accordance with the CM strategy as the least effective strategy. However, the highest efficiency (value 7) was adopted for the operation: continuous monitoring of the condition of all machines (e.g., noise, vibrations, temperature) (CBM). The value of MSI indicator is calculated as the sum of the value of activities by the number of implemented activities (4). \[MSI\ =\ \frac{\sum_{i=1}^{n}x_{i}}{n} \tag{4}\]  
The MSI indicator may take values from 1 to 7. Value 1 means mainly the CM strategy, value 3.5--PM strategy, value 7--CBM strategy.