Figure 4
The bar graph compares the number of articles by type of maintenance. It features seven horizontal bars. The x-axis represents the quantity, ranging from 0 to 25. The y-axis lists the types of maintenance addressed: Predictive Maintenance, Intelligent Predictive Maintenance, Maintenance 4.0, Prognostics and Health Management, Intelligent Maintenance, Preventive and Prognostic Maintenance, and Preventive Maintenance. Predictive Maintenance has the highest quantity, around 23, while the other types have significantly lower quantities, each around 1 to 2. All values are approximated.Number of articles by type of maintenance that was the main research focus of the analyzed article Source: Authors’ own elaboration (2025)