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  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>K. Verhal);</journal-title>
      </journal-title-group>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>Mathematical Methods for Assessing the Level of Cybersecurity and Digital Development of Countries⋆</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Kseniia Verhal</string-name>
          <email>itm.verhal@nupp.edu.ua</email>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Oksana Kushnirenko</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Oleksandr Bykonia</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Nazarii Romanovskyi</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Ivan Opirskyy</string-name>
          <email>ivan.r.opirskyi@lpnu.ua</email>
        </contrib>
      </contrib-group>
      <volume>000</volume>
      <fpage>0</fpage>
      <lpage>0002</lpage>
      <abstract>
        <p>The digital revolution and Industry 4.0 have significantly integrated information technology across economic sectors, driving rapid digitalization and economic transformation. However, this advancement also heightens cybersecurity risks, making national economies more vulnerable to cyber threats. Addressing these risks is essential for maintaining economic stability and safeguarding sensitive information. This study employs cluster analysis to assess cybersecurity and digital development levels at the national level. Using the National Cybersecurity Index (NCSI) and Digital Development Level (DDL) as key indicators, the k-means clustering algorithm was applied to categorize 71 countries into three clusters. The Elbow and Silhouette methods were used to determine the optimal number of clusters. The results identified three clusters with distinct cybersecurity preparedness: (1) high cybersecurity maturity (e.g., Moldova), (2) low cybersecurity preparedness (e.g., Libya), and (3) moderate cybersecurity development (e.g., Saudi Arabia). Countries in the highest cluster exhibit advanced cybersecurity strategies and well-established regulatory frameworks. In contrast, nations in the lower cluster face significant vulnerabilities due to weak regulations and limited cyber defense mechanisms. The findings emphasize the need for continuous cybersecurity enhancements, particularly in digitally emerging economies, to mitigate cyber threats and enhance national security.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;digital economy</kwd>
        <kwd>cybersecurity</kwd>
        <kwd>National Cybersecurity Index</kwd>
        <kwd>digital development</kwd>
        <kwd>cluster analysis</kwd>
        <kwd>kmeans</kwd>
        <kwd>Elbow method</kwd>
        <kwd>Silhouette method</kwd>
        <kwd>cyber threats</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <sec id="sec-1-1">
        <title>1.1. Relevance</title>
        <p>The integration of digital knowledge and information technology into all economic sectors is
driven by the digital revolution and Industry 4.0 [1, 2].</p>
        <p>The incorporation of information technology into various economic sectors is propelled by the
advancements of the digital revolution and Industry 4.0. The digital economy stands out as one of
the most dynamic, innovative, and influential economic models, playing a crucial role in driving
national economic growth [3]. This economy is defined by the exchange of goods and services
through digital platforms, following a unique operational structure. Its expansion is closely tied to
the development of information and communication technologies, leading to the rapid
transformation
and
integration
of related
industries
[4–6].</p>
        <p>However,
alongside these
advancements, the increasing reliance on digital technologies introduces significant cybersecurity
risks. The interconnected nature of digital infrastructures makes national economies more
susceptible to cyber threats, including data breaches, financial fraud, and critical system
disruptions. The complexity of these challenges underscores the need for proactive cybersecurity
measures to safeguard economic stability and protect sensitive information.</p>
        <p>Addressing cybersecurity threats linked to the use of information and communication
technologies is essential for organizations, governmental institutions, and individuals to effectively
pursue their developmental objectives. This underlines the necessity of strengthening
cybersecurity capabilities. By mitigating the negative consequences associated with digital
technology usage, governments can enhance their ability to maintain a robust level of
cybersecurity, ensuring a safer and more resilient digital landscape [7].</p>
      </sec>
      <sec id="sec-1-2">
        <title>1.2. Related work</title>
        <p>The concept of cluster analysis was initially introduced by R. C. Tryon in 1939. Tryon described
cluster analysis as: “A general logical procedure formulated as a procedure by which we group
objectively individuals into groups based on their similarities and differences” [8].</p>
        <p>Cluster analysis has been effectively utilized to solve data clustering challenges across various
fields, including goverment, manufacturing, finance, cyber security, urban development, industry,
sales, and marketing [9–11]. Extracting valuable insights from data in these areas is crucial for
enhancing services and increasing profitability. The data generated in real-world scenarios are
often large, unlabeled, and multi-dimensional, which complicates the clustering process.
Determining the number of clusters in such datasets cannot be easily achieved. As a result,
identifying the optimal number of clusters in real-world data with high density and dimensionality
is a challenging task for traditional clustering methods. This creates a significant hurdle for
conventional clustering techniques that require the number of clusters to be pre-specified as an
input.</p>
        <p>In recent studies, considerable focus has been placed on integrating cybersecurity technologies
and machine learning methods for monitoring and predicting IT security threats. In the study [12],
the author introduced a robust approach for detecting suspicious domains involved in advanced
persistent threat (APT) activities. The research evaluates various clustering algorithms and
highlights K-means as the most commonly used method. In the study [13], the author discusses the
growing importance of network security in today's digital landscape, particularly focusing on the
use of the K-means clustering algorithm in data mining for network security. In the study [14], the
author explores the use of cluster analysis for automating the matching of cyber threat intelligence
reports in an Internet-of-Vehicles (IoV) environment.</p>
      </sec>
    </sec>
    <sec id="sec-2">
      <title>2. Methods</title>
      <p>We will perform a clustering analysis of data that describe the levels of cybersecurity and
digitalization at the national level. To achieve this, we will analyze the National Cyber Security
Index, Digital Development Level.</p>
      <p>Data clustering algorithms are typically categorized into two main groups [15]: hierarchical
clustering algorithms and partitional clustering algorithms. Hierarchical clustering methods
organize data objects into clusters in a hierarchical structure, either through a bottom-up approach
(agglomerative method) or a top-down approach (divisive method). In the agglomerative method,
individual data points are iteratively merged based on their similarity. The divisive method, on the
other hand, starts with the entire dataset as a single cluster and iteratively divides it using data
object similarities until each object forms its own cluster, or until a predefined condition is met.
The hierarchical clustering algorithm generates a dendrogram, which visually represents the
process of merging (agglomerative) or splitting (divisive) data objects, illustrating the hierarchical
structure of clusters as the output of the cluster analysis. The dendrogram serves as a visual
depiction of the nested groupings of data objects, indicating the level of similarity at which each
grouping changes.</p>
      <p>K-means is the most popular clustering formulation in which the goal is to maximize the
expected similarity between data items and their associated cluster centroids [16].
K-means algorithm with K input parameters, N objects ware distributed into K clusters, that makes
a similar high similarity in the one cluster, low similarity between clusters. K-means algorithm
process as follows [17].</p>
      <p>The K-means clustering algorithm [15] is outlined below and consists of the following steps:
Input:

</p>
      <p>K: the number of the clusters.</p>
      <p>D: contain N object in data set.</p>
      <sec id="sec-2-1">
        <title>Output:</title>
      </sec>
      <sec id="sec-2-2">
        <title>Method:</title>
        <p></p>
        <p>K: clusters collection.</p>
      </sec>
      <sec id="sec-2-3">
        <title>1. Choose K objects as initial cluster centers; from D.</title>
        <p>2. Repeat.
3. Each object is assigned to the most similar clusters based on the mean value of the object in
the cluster.
4. Profile of the mean of each cluster, and calculating the mean of each cluster.
5. Until no change.</p>
        <p>The division of a set of objects into clusters should generally meet the following two
requirements:</p>
        <p>Objects within a single cluster should be similar in a certain sense.</p>
        <p>Clusters that are similar in a certain sense should be located close to each other.</p>
        <p>K-means clustering begins with the selection of k randomly positioned centroids (samples that
represent the center of a cluster). Each element is assigned to the nearest centroid. After the
assignment is made, the centroid is moved to the point calculated as the average of all the elements
assigned to it. Then, the assignment is performed again. This procedure is repeated until the
stopping condition is met.</p>
        <p>The algorithm works in such a way that it aims to minimize the mean squared deviation at the
points of each cluster:</p>
        <p>
          k S k
V = ∑ ∑ ( x j− μ i )2,
i= 1 x j ∈ S i
(
          <xref ref-type="bibr" rid="ref1">1</xref>
          )
where k is a number of clusters, S i is a obtained clusters, where i= 1,2 , … , k, μi are centroids of
the vectors, where x j ∈ S i.
        </p>
        <p>During the algorithm’s operation, at each iteration, the centroid of each cluster obtained in the
previous step is recalculated. Then, the vectors are reassigned to clusters based on which of the
new centroids is closest to the vector according to the chosen metric. The algorithm terminates
when, at any iteration, no change in the clusters occurs.</p>
        <p>For this research, two methods will be employed to determine the optimal number of clusters:
the Elbow method [18] and the Silhouette method.</p>
        <p>The Elbow method [18] is one of the earliest techniques for identifying the potentially optimal
number of clusters in a given dataset. Its fundamental concept involves initializing K = 2 and
incrementally increasing K by one until reaching a predefined maximum. The optimal number of
clusters, K, is then determined at the plateau point. This optimal K value is characterized by a sharp
decrease in the indicator value before reaching K, followed by minimal change beyond this point,
forming a distinct “elbow” shape. One of the limitations of the Elbow method is that when the
plotted curve is relatively smooth.</p>
        <p>The Silhouette method [19–21] has been discussed in sources where it is described as a
technique for estimating the potentially optimal number of clusters. This method evaluates
clustering quality by considering the average distance between a data point and others within the
same cluster, as well as comparing it to the average distance between different clusters. The
effectiveness of clustering is measured using the silhouette coefficient (S), which is calculated as
S =</p>
        <p>
          (b− a )
max (a , b )
,
(
          <xref ref-type="bibr" rid="ref2">2</xref>
          )
where a is the mean intra-cluster distance, b is a mean distance to the nearest neighboring
cluster.
        </p>
        <p>Based on the obtained Silhouette Score values, a conclusion is made about the optimal number
of clusters for further clustering s(i):


</p>
        <p>Close to 1 means that the point is well placed within its cluster.</p>
        <p>Close to 0 indicates that the point is on the boundary between two clusters.</p>
        <p>Close to –1 suggests that the point was likely assigned to the wrong cluster.</p>
        <p>This approach is commonly applied to determine the optimal number of clusters and assess
clustering performance in various scenarios.</p>
        <p>The quality of k-means clustering is measured through the within-cluster squared error
criterion [22].</p>
        <p>The k-means algorithm, Elbow method and the Silhouette method was implemented in Python
during the analysis of the indicators.</p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>3. Results</title>
      <p>According to the e-Governance Academy Foundation [23], the National Cybersecurity Index and
Digital Development Level indicators were used for clustering with the k-means method.</p>
      <p>The National Cyber Security Index (NCSI) is a global live index, which measures the
preparedness of countries to prevent cyber threats and manage cyber incidents. The NCSI is also a
database with publicly available evidence materials and a tool for national cyber security capacity
building.</p>
      <p>The NCSI focuses on measurable aspects of cyber security implemented by the central
government:</p>
      <sec id="sec-3-1">
        <title>1. Legislation in force—legal acts, regulations, orders, etc. 2. Established units—existing organisations, departments, etc. 3. Cooperation formats—committees, working groups, etc. 4. Outcomes—policies, exercises, technologies, websites, programmes, etc.</title>
        <p>The NCSI Score indicates the percentage that a country has achieved out of the maximum value
of the indicators. The maximum NCSI Score is consistently 100 (100%) regardless of any additions
or removals of indicators.</p>
        <p>
          NCSI = Country Points × 100 . (
          <xref ref-type="bibr" rid="ref3">3</xref>
          )
        </p>
        <p>Maximum Points</p>
        <p>The index table also shows the Digital Development Level (DDL). The DDL is calculated
according to the E-Government Development Index (EGDI) and Networked Readiness Index (NRI).
The DDL is the average percentage the country received from the maximum value of both indexes.
The average percentage of the maximum values for EGDI and NRI is displayed in the DDL.</p>
        <p>To create the dataset and perform clustering, a CSV file was generated containing information
about the country name, National Cybersecurity Index, and Digital Development Level.
A total of 71 countries were analyzed, all of which had corresponding values for the National
Cybersecurity Index and Digital Development Level indicators.</p>
        <p>To determine the optimal number of clusters, the necessary calculations were performed, and a
visualization using the Elbow method was created. The graphic was obtained from Sum Square
Error (SSE) calculation. The number of the cluster was determined by looking at the point position
on the “elbow” arm. [24].
As seen in Fig. 1, according to this method, the optimal number of clusters is 3.</p>
        <p>Let’s perform a verification using the Silhouette method (Fig .2 and 3). Based on the Silhouette
Score analysis, the most optimal number of clusters is 3. Although the first cluster appears to be
larger than the other two according to the visualized silhouette thickness, this clustering
configuration remains preferable. The Silhouette Score, which measures how well each data point
fits within its assigned cluster relative to other clusters, reaches its highest value for  = 3,
indicating a well-structured partitioning of the dataset.</p>
        <p>From a clustering quality perspective, the silhouette coefficient evaluates both intra-cluster
cohesion and inter-cluster separation. The relatively high silhouette score for k = 3 suggests that,
on average, countries within the same cluster are more similar, while the separation between
clusters remains significant. Although increasing the number of clusters to = 4 or  = 5 might lead
to finer segmentation, it also results in smaller clusters with decreased cohesion and lower
silhouette scores, making the overall structure less distinct.</p>
        <p>Additionally, when analyzing the silhouette thickness for different clusters at  = 3, it is evident
that one of the clusters is more populated compared to the others. However, this does not
necessarily indicate an imbalance in clustering but rather a natural distribution of the data, where
one segment may contain countries with similar cybersecurity and digital development
characteristics. Furthermore, compared to the models with  = 4 or  = 5, the three-cluster solution
ensures a relatively proportional distribution of countries while avoiding unnecessary
fragmentation.</p>
        <p>Thus, selecting = 3 is supported both by the quantitative metric (Silhouette Score) and
qualitative assessment of cluster interpretability, ensuring a meaningful and practical division of
countries based on their National Cybersecurity Index and Digital Development Level.
Using the proposed clustering algorithm, the dataset was successfully segmented into three distinct
clusters based on the National Cyber Security Index (NCSI) and Digital Development Level (Fig. 4).
The results of the clustering process are as follows (Table 2):</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>Conclusions</title>
      <p>The results of the cluster analysis conducted to assess the level of national cybersecurity and digital
development of countries allow us to examine these indicators in the context of grouping states
based on their cybersecurity levels. An important aspect is that countries with high, medium, and
low cybersecurity levels demonstrate different approaches to addressing digital resilience, which
influences their strategic initiatives and international cooperation in this field. In particular,
clustering helps identify patterns and significant differences in approaches to cybersecurity among
various countries.</p>
      <p>1. Cluster 0 includes 18 countries with a high NCSI range (71.67–98.33). The representative
country, Moldova (Republic of), is a fitting example due to its strong cybersecurity framework,
legislative advancements, and cybersecurity incident response mechanisms. Moldova has made
significant progress in strengthening its national cybersecurity framework, adopting
comprehensive policies and establishing key institutions to enhance its cyber resilience. The
country’s efforts reflect its commitment to protecting critical infrastructure and responding
effectively to cyber threats, especially given its strategic geopolitical position between the
European Union and Russia. A new national cybersecurity law, which will come into effect on
January 1, 2025, marks a major milestone in Moldova’s cybersecurity strategy. Developed with
support from the EU Cybersecurity Rapid Assistance Project, this legislation establishes clear
guidelines for cybersecurity governance. Under the new law, a competent national authority will
determine which institutions and service providers must meet specific cybersecurity standards.
These essential service providers will be required to report major cyber incidents to the national
authority, ensuring greater transparency and responsiveness in cyber threat management. The
legal framework is aligned with European best practices, reinforcing Moldova’s integration into
European cybersecurity structures. Vice Prime Minister Dumitru Alaiba, Minister of Economic
Development and Digitalization, emphasized that cybersecurity is a fundamental priority for
Moldova due to its vulnerable geopolitical position. The law reflects European standards, ensuring
that Moldova adopts advanced cybersecurity measures.</p>
      <p>Moldova has received strong international support in developing its cybersecurity capabilities.
On January 21, 2021, NATO launched a Cyber Incident Response Center for Moldova’s Armed
Forces. This initiative, developed in collaboration with the NATO Communications and
Information Agency and supported by the NATO Science for Peace and Security (SPS) Programme,
aims to minimize threats arising from cyber incidents, ensure rapid and effective recovery in case
of cyberattacks, and prevent future cyber threats through advanced cybersecurity mechanisms. In
2024, Moldova established two key institutions dedicated to cybersecurity: the National
Cybersecurity Agency, responsible for protecting critical government and public infrastructure
from cyberattacks, ensuring high-level security of networks and information systems in both
public and private sectors, and the National Institute for Cybersecurity Innovation (“Cybercor”),
focused on cyber threat prevention, research, and innovation in digital security. These institutions
will play a crucial role in enhancing Moldova’s cybersecurity preparedness, resilience, and
innovation, ensuring a secure digital ecosystem for both public and private entities. Moldova’s
recent cybersecurity advancements demonstrate a proactive and strategic approach to digital
security. By adopting a new cybersecurity law, strengthening cooperation with NATO and the EU,
and establishing key institutions, Moldova is positioning itself as a leader in cybersecurity among
emerging economies. These developments highlight a structured, well-coordinated national effort
to combat cyber threats and align Moldova’s cybersecurity policies with European and global
standards.</p>
      <p>Countries in the cluster 0 exhibit well-established cybersecurity strategies, comprehensive
infrastructure, and government initiatives focused on digital resilience. Notably, Ukraine is also
part of this cluster, signifying its relatively high cybersecurity preparedness.</p>
      <p>2. Cluster 1: Low National Cyber Security Index. Cluster 1 consists of 27 countries with an NCSI
range of 4.17–40.83, representing nations with relatively low cybersecurity preparedness. Libya is
the representative country of this cluster. Libya, as a country experiencing political instability and
conflicts, faces numerous challenges in the field of cybersecurity. Libya is one of the most
vulnerable countries to significant cybersecurity threats in 2023, ranking 90th globally. This high
risk is attributed to insufficient security measures against cybercrimes, making them highly
susceptible to attacks. These country has weak or entirely absent legislation against cybersecurity
threats, putting sensitive transactions at significant risk[25–28].</p>
      <p>The lack of a stable government and centralized control complicates the development and
implementation of effective cyber protection strategies, making state and private information
systems vulnerable to cyber threats [29]. However, despite these difficulties, Libya demonstrates
some potential in cybersecurity development. The presence of an educated youth and a growing
interest in information technology create prerequisites for the formation of specialists in this field.
Additionally, international organizations and partners provide support to Libya in strengthening its
cybersecurity infrastructure, contributing to a gradual improvement of the situation. One of the
key regulatory bodies in cybersecurity is NISSA (National Information Security and Safety
Authority), which has released the NISSA Policy Guide. However, Libya still lacks a comprehensive
cybersecurity strategy, though NISSA has been mandated to develop one in cooperation with the
Ministry of Communications and Informatics. Despite the absence of a unified strategy, the
country has specialized institutions addressing cybersecurity issues. Notably, under the Ministry of
Interior, the “Administration for Combating IT Crimes” is responsible for investigating
cybercrimes. Additionally, the national cybersecurity incident response team, Libya-CERT (Libyan
Computer Emergency Response Team), operates under NISSA. It was established with the support
of the International Telecommunication Union (ITU) and is responsible for preventing, detecting,
and mitigating cyber threats at the national level.</p>
      <p>However, despite ongoing efforts, certain aspects of its cybersecurity policies may still be
developing. Countries in this group likely have fragmented cybersecurity frameworks, limited
resources allocated to cyber defense, and emerging regulatory frameworks.</p>
      <p>Cluster 2: Moderate National Cyber Security Index. Cluster 2 contains 26 countries with an
NCSI range of 47.5–70.83. The representative country, Saudi Arabia, typifies this group as it is in a
transitional stage of cybersecurity development.</p>
      <p>Saudi Arabia has been actively working to improve its cybersecurity; however, its relatively low
cybersecurity index may be attributed to several factors. Firstly, while the country has made
significant progress in digitalizing government services, the rapid pace of digital transformation
may outstrip the development of corresponding cybersecurity measures. Secondly, as a major oil
producer, Saudi Arabia is an attractive target for cyberattacks, necessitating continuous
advancements in defensive strategies. Additionally, although the country is implementing digital
governance strategies such as “Saudi Vision 2030” to enhance citizens' quality of life, these
initiatives may take time to achieve full effectiveness in cybersecurity.</p>
      <p>An analysis of Saudi Arabia’s cybersecurity framework has highlighted key risks associated
with its development model. While assessments based on International Telecommunication Union
(ITU) standards have yielded relatively positive results, Saudi Arabia has demonstrated a catch-up
approach to cybersecurity development and continues to experience challenges in national cyber
defense. Some of these challenges are global in nature, such as legislative gaps, while others stem
from the specifics of the national governance model. The most prominent risks include an
imbalance between the civilian and military cybersecurity sectors, regional disparities in
cybersecurity readiness, and weak integration of the local hacker community into the national
cybersecurity framework [30].</p>
      <p>Nations in this cluster have moderate cybersecurity strategies, often influenced by economic,
political, and technological challenges that affect their ability to implement robust cybersecurity
measures.</p>
      <p>According to the results of the cluster analysis, countries with a high level of cybersecurity
(Cluster 0) demonstrate well-developed infrastructure, clearly defined national strategies, and
effective government policies in the field of digital security. The selection of Moldova as the
representative of this cluster highlights the importance of having appropriate legislation,
international support, and strategic institutions for creating a stable and resilient cybersecurity
ecosystem. In countries of this cluster, a high level of organizational maturity in countering cyber
threats is observed, enabling them to effectively respond to incidents and implement innovative
technologies to enhance cyber resilience.</p>
      <p>On the other hand, countries with a low level of cybersecurity (Cluster 1) face numerous
challenges, including political instability, the absence of or weak legislation, and limited resources
for developing national cybersecurity strategies. The example of Libya, the representative of this
cluster, demonstrates how crucial international assistance is for strengthening cybersecurity
infrastructure, as well as creating specialized organizations capable of responding to cyber threats
in a timely manner. Considering the limited capacity of such countries to implement effective
strategies, further cooperation with international partners is critical to improving their
cybersecurity defenses.</p>
      <p>Given the identified characteristics, it is recommended that countries with low levels of
cybersecurity, such as Libya and others with similar issues, actively seek international support to
establish basic cybersecurity standards and create specialized institutions for responding to cyber
incidents. An essential step is also strengthening the training and preparation of specialists, which
will help reduce the risks of cyber threats in these countries.</p>
      <p>Countries with a moderate level of cybersecurity, such as Saudi Arabia, should focus on
improving their cybersecurity strategies by enhancing the integration of civilian and military
sectors, as well as strengthening cooperation with international partners to achieve sustainable
development in digital security.</p>
      <p>Declaration on Generative AI
While preparing this work, the authors used the AI programs Grammarly Pro to correct text
grammar and Strike Plagiarism to search for possible plagiarism. After using this tool, the authors
reviewed and edited the content as needed and took full responsibility for the publication’s content.
[5] M. Chyzhevska, et al., Dual Impact of Crypto Industry Technologies on the Energy Poverty, in:
Cybersecurity Providing in Information and Telecommunication Systems, vol. 3421, 2023, 293–
299.
[6] M. Chyzhevska, et al., Behavioral Biometry as a Cyber Security Tool, in: Cybersecurity</p>
      <p>Providing in Information and Telecommunication Systems, vol. 3188, 2021, 88–97.
[7] Z. Homburger, The Necessity and Pitfall of Cybersecurity Capacity Building for Norm
Development in Cyberspace, Global Society 33 (2019) 224–242.
doi:10.1080/13600826.2019.1569502
[8] R. C. Tryon, Cluster Analysis: Correlation Profile and Orthometric (Factor) Analysis for the</p>
      <p>Isolation of Unities in Mind and Personality, Edwards Brothers, Ann Arbor, 1939.
[9] A. M. Ikotun, et al., K-Means Clustering Algorithms: A Comprehensive Review, Variants
Analysis, and Advances in the Era of Big Data, Information Sciences, 622 (2023) 178–210.
doi:10.1016/j.ins.2022.11.139
[10] A. Belhadi, et al., Space–Time Series Clustering: Algorithms, Taxonomy, and Case Study on</p>
      <p>Urban Smart Cities, Eng. Appl. Artificial Intell. 95 (2020).doi:10.1016/j.engappai.2020.103857
[11] D. Parnes, A. Gormus, Prescreening Bank Failures with K-Means Clustering: Pros and Cons,</p>
      <p>Int. Rev. Financial Anal. 93 (2024) 103222. doi:10.1016/j.irfa.2024.103222
[12] G. Yan, et al., AULD: Large Scale Suspicious DNS Activities Detection via Unsupervised</p>
      <p>Learning in Advanced Persistent Threats, Sensors 19(14) (2019) 3180. doi:10.3390/s19143180.
[13] C. Bu, Network Security Based on K-Means Clustering Algorithm in Data Mining Research, in:</p>
      <p>
        Advances in Computer Science Research, vol. 83, 2018, 642–645. doi:10.2991/snce-18.2018.130.
[14] G. Raptis, C. Katsini, C. Alexakos, Towards Automated Matching of Cyber Threat Intelligence
Reports based on Cluster Analysis in an Internet-of-Vehicles Environment, in: IEEE
International Conference on Cyber Security and Resilience (CSR), 2021, 366–371.
doi:10.1109/CSR51186.2021.9527983
[15] A. K. Jain, et al., Data Clustering: A Review, ACM Computing Surveys, 31(
        <xref ref-type="bibr" rid="ref3">3</xref>
        ) (1999) 264–323.
      </p>
      <p>doi:10.1145/331499.331504
[16] N. Slonim, et al., Hartigan’s K-Means Versus Lloyd’s K-Means—Is It Time for a Change?, in:
Proceedings of the Twenty-Third International Joint Conference on Artificial Intelligence,
2013, 1677–1684.
[17] J. Cui, et al., Research on K-Means Clustering Algorithm and its Implementation, in:</p>
      <p>Proceedings of ICCSEE, 2013. doi:10.2991/iccsee.2013.452
[18] D. J. Ketchen, C. L. Shook, The Application of Cluster Analysis in Strategic Management
Research: an analysis and critique, Strategic Manag. J. 17(6) (1996) 441–458.
doi:10.1002/(SICI)1097-0266(199606)17:6&lt;441::AID-SMJ819&gt;3.0.CO;2-G
[19] P. J. Rousseeuw, Silhouettes: A Graphical Aid to the Interpretation and Validation of Cluster</p>
      <p>Analysis, J. Computat. Appl. Math. 20 (1987) 53–65. doi:10.1016/0377-0427(87)90125-7.
[20] O. Arbelaitz, et al., An Extensive Comparative Study of Cluster Validity Indices, Pattern</p>
      <p>
        Recognition, 46(
        <xref ref-type="bibr" rid="ref1">1</xref>
        ) (2013) 243–256. doi:10.1016/j.patcog.2012.07.021
[21] R. Tibshirani, et al., Estimating the Number of Clusters in a Data Set via the Gap Statistic, J.
      </p>
      <p>
        Royal Statistical Society: Series B (Statistical Methodology), 63(
        <xref ref-type="bibr" rid="ref2">2</xref>
        ) (2001) 411–423.
doi:10.1111/1467-9868.00293
[22] C. Yuan, H. Yang, Research on k-Value Selection Method of k-Means Clustering Algorithm,
      </p>
      <p>
        Multidisciplinary Sci. J. 2(
        <xref ref-type="bibr" rid="ref2">2</xref>
        ) (2019) 226–235. doi:10.3390/j2020016
[23] E-Governance Academy Foundation. URL: https://ncsi.ega.ee/methodology
[24] H. Hestry, R. Rasyidah, Determining the Appropriate Cluster Number Using Elbow Method for
      </p>
      <p>K-Means Algorithm, in: EAI Proceedings, 2020.
[25] Y. Kostiuk, et al., A System for Assessing the Interdependencies of Information System Agents
in Information Security Risk Management using Cognitive Maps, in: 3rd Int. Conf. on Cyber
Hygiene &amp; Conflict Management in Global Information Networks (CH&amp;CMiGIN), Kyiv,
Ukraine, vol. 3925, 2025, 249–264.
[26] Y. Kostiuk, et al., Models and Algorithms for Analyzing Information Risks during the Security
Audit of Personal Data INFORMATION System, in: 3rd Int. Conf. on Cyber Hygiene &amp; Conflict
Management in Global Information Networks (CH&amp;CMiGIN), Kyiv, Ukraine, vol. 3925, 2025,
155–171.
[27] S. Shevchenko, et al., Information Security Risk Management using Cognitive Modeling, in:
Cybersecurity Providing in Information and Telecommunication Systems II, CPITS-II, vol.
3550 (2023) 297–305.
[28] S. Zybin, et al., Approach of the Attack Analysis to Reduce Omissions in the Risk
Management, in: Cybersecurity Providing in Information and Telecommunication Systems,
CPITS, vol. 2923 (2021) 318–328.
[29] V. Astapenya, et al., Conflict Model of Radio Engineering Systems under the Threat of
Electronic Warfare, in: Cybersecurity Providing in Information and Telecommunication
Systems, CPITS, vol. 3654 (2024) 290–300.
[30] L. Cukanov, Saudi Arabia National Cyber Security System: Specificity and Development Risks,
in: Bulletin of Kemerovo State University, Series: Political, Sociological and Economic
Sciences, 2022, 435–443. doi:10.21603/2500-3372-2021-6-4-435-443</p>
    </sec>
  </body>
  <back>
    <ref-list>
      <ref id="ref1">
        <mixed-citation>
          [1]
          <string-name>
            <surname>A.</surname>
          </string-name>
           Fagarazzi,
          <source>Impact of Digital Development Level on National Cybersecurity Index</source>
          , Poslovna izvrsnost,
          <volume>18</volume>
          (
          <issue>2</issue>
          ) (
          <year>2024</year>
          )
          <fpage>37</fpage>
          -
          <lpage>61</lpage>
          . doi:
          <volume>10</volume>
          .22598/pi-be/
          <year>2024</year>
          .18.2.
          <fpage>37</fpage>
        </mixed-citation>
      </ref>
      <ref id="ref2">
        <mixed-citation>
          [2] О. 
          <article-title>Kushnirenko, The Industry of Ukraine Facing the Challenges of Industry 4.0: Evaluation of Limitations and Policy TASKS</article-title>
          , Economy of Ukraine,
          <volume>63</volume>
          (
          <year>2020</year>
          )
          <fpage>53</fpage>
          -
          <lpage>71</lpage>
          . doi:
          <volume>10</volume>
          .15407/economyukr.
          <year>2020</year>
          .
          <volume>05</volume>
          .053
        </mixed-citation>
      </ref>
      <ref id="ref3">
        <mixed-citation>
          [3]
          <string-name>
            <surname>L.</surname>
          </string-name>
           
          <article-title>Guo, The Impact Mechanism of the Digital Economy on China's Total Factor Productivity: An Uplifting Effect or a Restraining Effect?</article-title>
          ,
          <source>South China J. Econom</source>
          .
          <volume>40</volume>
          (
          <year>2021</year>
          )
          <fpage>9</fpage>
          -
          <lpage>27</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref4">
        <mixed-citation>
          [4]
          <string-name>
            <given-names>M.</given-names>
             
            <surname>Chyzhevska</surname>
          </string-name>
          , et al.,
          <source>Tokenomics and Perspectives of Proof of Stake, in: Digital Economy Concepts and Technologies</source>
          , vol.
          <volume>3665</volume>
          ,
          <year>2024</year>
          ,
          <fpage>61</fpage>
          -
          <lpage>69</lpage>
          .
        </mixed-citation>
      </ref>
    </ref-list>
  </back>
</article>