# Overall Equipment Effectiveness: Systematic Literature Review and Overview of Different Approaches
## 3 Results  
RQ (1). What is the focus of the current research effort in the OEE domain? The bibliometrix R-package was used to analyze the 186 articles from the two electronic databases. This packaged, which is written in the R language, provides a set of tools for quantitative studies in bibliometrics and scientometrics [24]. Using this program, the data extracted from WoS and Scopus were consolidated to perform a comprehensive bibliometrics analysis of the current research effort pertaining to OEE. Table 2 shows a general data summary from the 186 articles. Despite a 24 years timespan, scientific productivity increased only in the later years. The results show that more than 50% of the publications regarding OEE were published in the last five years, indicating that interest in the OEE indicator has increased, i.e., by 9.1% in 2015, 9.1% in 2016, 10.8% in 2017, 14.0% in 2018 and 16.7% in 2019. Thus, far, an increase of 3.2% has been reported for 2020. Figure 2 presents (a) the number of articles per year since 1996 until 9 April 2020, revealing an increasing interest in the subject and (b) the top 10 journals with increasing publications over time. Figure 1: Preferred reporting items for systematic review and meta-analysis (PRISMA) flow chart. The total number of journals published regarding OEE was 102. Journals pertaining primarily to manufacturing or maintenance issues were not the only ones that focused on the OEE indicator. Evidence shows that an increasing number of journals are focusing on sustainability, business, logistics, mining, etc. The current effort to spread the topic based on contributor and geographical location is shown in Figure 3. Europe is the continent with the most publications (45%) followed by Asia (26%), America (7%) and Africa (5%), as shown in Figure 3a. Figure 3b presents the top 10 countries in terms of single country publication (SCP) and multiple country publication (MCP). More than 80% of the publications were written by authors belonging to the same country; all the scientific productions in India were based entirely on SCPs, unlike the UK and Spain, who collaborative with other countries. Figure 3c indicate the top 10 most productive authors, including the number of articles (N articles) and total citations per year (TC per year). Greek author [PERSON] was the first in the top 10, with 83.33% of his publications reporting cases in which OEE was applied to different production industries, e.g., croissant production lines [25], ice cream production lines [26] and production plants of Italian cheese [27] to identify potential opportunities for improving production systems. [PERSON] and [PERSON] published four articles, whereas the other authors from the top 10 published three articles each. Some of them have developed new models based on OEE, whereas others have applied the indicator in different industries to measure equipment, process or resource effectiveness. \begin{table}
\begin{tabular}{c c} \hline \hline
**Timespan** & **1996–2020** \\ \hline Sources (journals) & 102 \\ Documents & 186 \\ Average citations per document & 16.57 \\ \hline Author keywords & 554 \\ Keywords plus & 434 \\ \hline Authors & 450 \\ Authors of single-author documents & 25 \\ Authors of multi-author documents & 425 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: General data summary. Figure 2: Basic data analysis of (**a**) number of articles per year and (**b**) Top 10 journals. Three inclusion criteria were used for the analysis in this study. (a) Criteria II--include papers that are literature reviews and/or are related specifically to OEE and its application; (b) Criteria I2--studies that mention OEE-based models; (c) Criteria I3--papers that only use the OEE to verify an improvement or change in any process (Table 3). Approximately 20% of the articles contributed scientifically to the modification or new development of models based on the original OEE (Figure 4).