*3.1. Research Objectives*

The general objective of this study was to analyze the scientific literature on ADIN indexed in the WoS database. This general objective is articulated in the following specific objectives:


The research questions posed are


### *3.2. Research Design*

The research methodology adopted in this study to achieve the proposed objectives was bibliometry. This choice is justified in the scientometric potentialities linked to the actions of searching, recording, analyzing, and predicting scientific literature [38]. Similarly, the guidance and considerations of experts in this type of study were followed [39].

Specifically, this work was based on the analysis of co-words [40] and various bibliometric indicators such as the h-index, taken as a reference, in addition to other indices (g, hg, q2) [41]. This gave rise to the creation of node maps whose interpretation determined the performance and position of conceptual subdomains alluding to ADIN. In addition, the analytical treatment delimited the thematic development of these concepts in WoS [42]. From this database, we used the complete record in order to obtain as much information as possible, in order to have the most relevant data to perform the co-word analysis [43].

### *3.3. Procedure and Data Analysis*

This investigation was carried out following various actions that specified the following procedures: (a) selection of the database (WoS), (b) determination of the keywords ("addiction" and "internet") after consultation in specialized thesauri (ERIC and UNESCO) and in the information provided in the Special Issue of the *International Journal of Environmental Research and Public Health*, and (c) construction of a precise search equation to obtain significant results ("addiction\*" [TOPIC] AND "internet" [TOPIC]) and report documents containing both terms in different metadata (title, abstract, and keywords).

The first search action compiled a scientific volume of 5776 publications. In addition, the entire report was analyzed to eliminate repeated documents, those belonging to the year 2020 and the poorly indexed ones. After this, an analysis unit of 5644 publications remained, as a result of the configuration of various production indicators with their respective inclusion criteria (Table 1).


**Table 1.** Production indicators and inclusion criteria.

To improve the understanding and visualization of the different actions carried out, the following flow chart was established following the protocols of the PRISMA-P matrix (Figure 1).

**Figure 1.** Flowchart according to the PRISMA Declaration.

The documents obtained were analyzed with various programs (Analyze Results, Creation Citation Report, and SciMAT). The first two tools are provided by WoS and were used to obtain data concerning the year, authorship, country, type of document, institution, language, means of publication, and most cited documents. For the structural and dynamic development of a longitudinal nature of the scientific volume, SciMAT was used, under the considerations of the experts [44].

With SciMAT, a co-word analysis of the topics was carried out through the following processes:


was established (PX = 1996-2019). The number of matching keywords determined the strength of association between the configured periods.

• Performance: In this process, a set of production indicators associated with inclusion criteria that determine the scientific works that become part of the study were delimited (Table 2).


**Table 2.** Production indicators and inclusion criteria.

#### **4. Results**

#### *4.1. Performance and Scientific Production*

The evolution of the 5644 documents in the scientific production on ADIN has been constant and continuous over time, showing an exponential growth from its beginnings until the year 2019 (Figure 2). In this sense, and according to the Price law about growth of scientific information, visualization of the distribution of publications on internet addiction doubled in its development 10 years after its first publication. At present, productivity on the subject is in a phase of linear growth.

**Figure 2.** Evolution of scientific production of the keywords "addiction" and "internet" (ADIN) in the Web of Science (WoS).

The language chosen by the various authors for the presentation of the academic results was English (Table 3).


**Table 3.** Scientific language used in ADIN.

The main area of knowledge in ADIN studies is psychiatry, distanced considerably from other areas of knowledge (Table 4).


**Table 4.** Research areas.

The type of document mainly used by the various scientists are articles (Table 5).


**Table 5.** Document types.

Nottingham Trent University is the leading organization in ADIN studies (Table 6).


The most prolific author is Griffinths, M.D., with considerable scientific output on ADIN (Table 7).



**Table 7.** *Cont.*


The main source of presentation of studies on ADIN are, with similar productions, *Computers in Human Behavior* and the *Journal of Behavioral Addictions* (Table 8).


The country with the greatest interest in production on ADIN is the United States (Table 9).


**Table 9.** Countries.

The reference author for the scientific community in relation to the subject of ADIN, in terms of number of citations, is Davis (2001), followed at a short distance by Morahan-Martin and Schumacher (2000) and Block (2008) (Table 10).


**Table 10.** Most cited articles and main conclusions.

#### *4.2. Structural and Thematic Development*

The evolution of keywords shows information about the number of keywords in each of the established time intervals, the number of matching keywords between the periods, and the number of keywords leaving and entering a certain period with respect to another. The studies on ADIN, taking into account the evolution of keywords in scientific production, mark a settled and consolidated line of research, given that the level of coincidence between periods was between 40% and 50% (Figure 3).

**Figure 3.** Continuity of keywords between contiguous intervals.

The academic performance in the established periods offers the subjects with the greatest bibliometric indicators, using the h-index as the main reference, and completing this information with the g-index, hg-index and q2-index, in addition to the number of citations. On the subject of ADIN, the subjects with the highest bibliometric indicators varied between periods. In the first time period (1996–2010), the topic with the highest bibliometric indicator was "addiction"; in the second time period (2011–2014) it was "prevalence"; in the third time period (2015–2017) it was "depression" and "addiction"; and in the last time period (2018–2019) it was "adolescents". This shows changes in the interests of researchers in this field of study. We also observed the changes between periods of the topics of greatest interest to researchers, showing the main lines of research in each of the established time intervals (Table 11).


**Table 11.** Thematic performance.


**Table 11.** *Cont.*

The diagrams of the intervals developed show data on the importance of each of the themes in the different periods. For this purpose, a grouping process was developed, according to Callon's indicators, which assesses the degree of interaction of a network with respect to other networks, from two axes: centrality, which analyses the strength of the relationship of external links with other topics, where it shows the importance of the development of a topic in a field of research; and density, which assesses the internal strength of the network, analyzing the internal links between the key words that are grouped around a specific topic, giving information on the degree of development of a field of study. In the first period (1996–2010), the driving themes were "addiction", "prevalence", "symptoms", "health-care", and "sensation-seeking". In the second period (2011–2014), the themes were "prevalence", "children", "computer-use", and "loneliness". In the third period (2015–2017), themes were "depression", "addiction", "DSM-5", "functional-connectivity", "self-esteem", "children", and "validation". In the last period (2018–2019), themes were "adolescents", "self-esteem", "impulsivity", "children", and "video-games". From this last period, we should also highlight the themes "international-consensus", "stress", "risk", "life", and "internet-use", given that their location in the diagram makes them unknown themes, as they may be the next references in the next few years in this field of study, or they may disappear. Generally speaking, the interests of ADIN researchers are focused on aspects related to adolescents, children, frequency, and addiction, as these are the issues that most appear in the motor themes of the diagram (Figure 4).

**Figure 4.** ADIN's strategic diagram by h-index. Note: (**a**) interval 1996–2010; (**b**) interval 2011–2014; (**c**) interval 2015–2017; (**d**) interval 2018–2019.

#### *4.3. Thematic Evolution of the Terms*

The thematic evolution offers the strength of the relationship maintained between the themes of the various intervals generated according to the Jaccard index. The development is generated if

a theme of a particular interval shares keywords or themes with the subsequent or previous periods. The greater the number of keywords between the two themes of consecutive intervals, the more solid its evolution will be. The possible connections are continuous line, where its connection is thematic, and discontinuous line, whose connection is by keywords. The thickness of the lines shows the strength of the relationship between the themes. The data showed a conceptual gap in the thematic evolution in the ADIN study, as there was no keyword that was repeated in all the established periods. Even so, there were themes that were repeated in at least two or more periods. The timeline with the greatest connecting force was the one established between "prevalence-prevalence-depression-adolescent", being the basis of the studies on the research topic. There were other strong connections, such as those established between "play-play", from the second and third period, and "impulsivity-impulsivity" or "self-esteem" from the third and fourth period. In addition, Figure 5 shows that there were an even number of thematic connections and keyword connections. The studies on ADIN had an established basis, focusing mainly on people under 18 years of age and the different pathologies caused by internet use addiction.

**Figure 5.** Thematic evolution by h-index.

#### *Int. J. Environ. Res. Public Health* **2020**, *17*, 2753
