# Taxonomy of Scheduling Problems with Learning and Deterioration Effects
## 3 Results  
### Bibliometric Analysis  
The first interesting output of this review is related to a bibliometric study in order to build on a high-level perspective of the publications in terms of the most discussed topics, authors' nationality, and journals. Bibliometrics consists of the use of quantitative research methods to analyze bibliographic material, with a view of mapping research works [18; 19; 20]. Bibliometric analysis also serves to evaluate research performance (per country, university, etc.) and allows us to understand relations between scientists. From an academic point of view, applying bibliometric analysis to map research works on scheduling with learning and deteriorating effects in processing times will help both researchers and practitioners better understand the advances and trends in the field, as well as enable them to make decisions and take action in a more informed way [21]. From a static perspective (i.e., printing year) on the proposed analysis strategy, this literature review includes articles published from 1999 (first official publication on the topic) to December 2021. [PERSON] [6] published the first study. His paper can be considered the starting point of research activities related to this field. The number of articles has since grown, with a peak in 2013 (see Figure 2). There has been a rising trend in this area since 2009, with an average of 32 articles per year in the period 2009-2021. This result may be explained by the fact that around 2011, the concept of the fourth industrial revolution appeared. Despite the high levels of automation, this has brought the challenge of integrating humans into production systems and redefining their roles. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**RQ** & **Section** & **Methodologies** & **Outputs** \\ \hline
1 & Section 3.1 & Bibliometric analysis of the final short-list articles (from Scopus and Web of science). & Identify publications by year, country, distribution of main publishing journals and thematic trends. \\ \hline
2, 3 & Section 3.2 & & Recognize the common system configuration approach, the types of objective functions and the criteria taken into consideration. \\ \hline
4 & Section 3.3 & Classification, descriptive analysis, and content analysis of short-listed articles. & Identify relevant models proposed to address the learning and deterioration effect regarding scheduling problems. \\ \hline
5 & Section 3.4 & & Recognize solution methods employed in these problems and the frequency of use. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Approaches to address the research questions. We note that all short-listed articles are distributed in 95 journals, 32 of which contain 80% of all publications. Figure 3 presents the most relevant journals in this area by the number of publications. Each of these journals published ten or more articles, meaning 56.7% of the total number of publications. _Applied Mathematical Modelling_ (9.7%), _Computers and Industrial Engineering_ (9.5%), and _International Journal of Advanced Manufacturing Technology_ (6.4%) are the journals with the highest number of articles. To deepen our investigation of the short-listed papers, we used VOSviewer software [22] to analyze the co-occurrences of a country's authors. Figure 4 shows the most productive countries in this field (with five or more articles), of which China is in the lead, with 220 articles. There are four clusters, the green cluster (China, USA, and Poland), the red cluster (Turkey, Iran, Canada, France, and Australia), the  
Figure 3: Frequency per journal (journal with ten contributions or more). Figure 2: Frequency of publications per year. blue cluster (Taiwan and Tunisia), and finally, Hong Kong in yellow. In general, the Asian countries are interested in research in this field (even given the thick lines, high levels of cooperation between China-Taiwan and China-Hong Kong can be deduced).