## 2 Efficiency in PM: The PMO  
The PMO is an organizational unit responsible for centralized and coordinated project management that carries out distinct functions and performs specific roles in PM [16], adapting its structure to the overall organizational framework [17]. Refs [18; 19] shed light on the evolving roles and changing responsibilities of PMOs over time. Additionally, [20] emphasizes the PMO's crucial role in facilitating knowledge transfer among similar projects. By operating centrally, the PMO plays a pivotal role in fostering the exchange of insights among stakeholders. According to [21], a PMO model can take on different forms, serving as a service provider, a control center, or a management partner. In summary, the PMO can be categorized as an entity that offers various services, ranging from maintaining standardization systems to resource management, all with the overarching objective of supporting executive management and bolstering the project portfolio [22]. According to [23], the earliest implementations of PMO in companies date back to the early 1990s. [22] point out that the majority, approximately 65%, of the implementations encountered during the study occurred after the 2000s. Consequently, uncertainties persist regarding the methods and techniques available for centralizing PM activities [24]. Centralized PM activities in PMO-type entities can be a critical success factor in projects, given their ability to standardize procedures and focus on objectives linked to deadlines, costs, and scope compliance. Another critical success factor in PM is the PMO's position in the organizational structure, which must be autonomous and cross-functional to be effective [25]. Assessing and managing the efficiency of PMOs can play a pivotal role in enhancing project outcomes. PMOs with a higher efficiency index yield improved compliance with deadlines, costs, and scope, enhancing overall project effectiveness [26]. When strategically positioned, the PMO enhances results [27] and fosters organizational learning [28]. This improvement results from acquiring superior knowledge, implementing standardized processes, and enhancing training. As [29] emphasized, there should be seamless integration between success factors and governance. Despite the acknowledged necessity of efficiency control, the existing literature, according to [30], has predominantly focused on PMO functionalities rather than tangible outcomes. Another gap in the literature pertains to uncertainties surrounding the significance of PMOs [31] and the integration of multiple roles [32]. A recent gap relates to the ambiguity surrounding the decision-making processes within PMOs [16]. To characterize the evaluation variables of a PMO, one must first discern how the PMO operates within each organization [7]. By establishing measurable parameters and metrics, the PMO can showcase its efficiency [33], overseeing performance in every activity and project phase. With a comprehensive view of project management, the PMO can pinpoint efficiencies at various process stages. Practical and significant results, considering both internal and external environmental variables, can contribute to managing the PMO's efficiency. Internal variables can be managed within the system's control, while external variables, often referred to as natural states, remain beyond management's influence and are contingent upon external forces, such as market dynamics and economic growth [34]. Typically, a PMO succeeds in reducing project duration and costs while simultaneously maintaining scope and expected quality [35]. It also advances project management maturity within organizations [36]. Assessing a PMO's impact on project efficiency can deliver quantitative and qualitative benefits, which requires comprehension of the context in which the PMO operates and its evolving maturity level. This understanding helps define how a PMO engages in projects, consequently affecting its efficiency and, by extension, the project's efficiency [37].