*3.3. Thematic Analysis of Literature and Research Interests Over Time*

Figure 2, which was generated by the analysis of content of abstracts and titles, provides an illustration of the most frequently co-occurred groups of terms. There were four clusters emerging from 458 terms with co-occurrence at least 30 times. Red cluster points out indicators of pulmonary function tests, such as forced vital capacity (FVC), forced expiratory volume in one second (FEV1), peak expiratory flow (PEF), and treatment for different asthma conditions, including inhaled corticosteroids (ICS), mometasone furoate dry powder inhaler (MF-DPI), salmeterol, etc. Yellow cluster focuses on common questionnaires for measuring asthma-related quality of life, namely Asthma Quality of Life Questionnaire (AQLQ), Pediatric Quality of Life Inventory (PedsQL) and Living with Asthma Questionnaire (LWAQ). Blue nodes reveal various approaches of intervention for asthma, while green cluster refers to comorbidity of asthma and factors associated with quality of life among asthmatics.

**Figure 2.** Co-occurrence of most frequent terms in titles and abstracts. Note: the colors of the nodes indicate principle components of the data structure; the node size was scaled to the keywords' occurrences. Abbreviations: (red cluster) fvc—forced vital capacity, fev1—forced expiratory volume in one second, pef—peak expiratory flow, pefr—peak expiratory flow rate, ahr—airway hyperresponsiveness, ics—inhaled corticosteroids, mf dpi—mometasone furoate dry powder inhaler; (yellow cluster) qol—quality of life, aqlq—Asthma Quality of Life Questionnaire, aqlq s—Asthma Quality of Life Questionnaire (Standardized), paqlq—Pediatric Asthma Quality of Life Questionnaire, pedsql—Pediatric Quality of Life Inventory, lwaq—Living with Asthma Questionnaire; (green cluster) mcs—multiple chemical sensitivity.

By applying Latent Dirichlet Allocation for the abstracts, we constructed research articles into ten major topics (Table 4, Figure 3). We extracted a list of papers most likely to be associated with each topic identified, then reviewed the titles and abstracts of the most cited papers within each group to determine the name for each topic. The topic number was assigned by the number of papers belonging to the topic in the last five years. The *n* (%) is the total number and percentage of papers classified into the topic over the research period. We also rank the topics by highest literature volume produced in the last five years. According to the results of the LDA analysis, asthma control and self-management education interventions was the topic of most interest over time as well as in the last five years, accounting for over one-fifth of the literature volume. Meanwhile, the total number of studies on application and impact of non-medical treatment og asthma have received relatively little attention.

In addition, Figure 3 provides an evident illustration of the trend in the interest in each topic throughout the research period. Despite being ignored in the first years, research on asthma control and education interventions for asthmatics (Topic 1) has increased rapidly and become the research topic that covers a large body of the literature, with a robust rise, especially in recent years. Studies into specific types of asthma (Topic 2 and Topic 7), and the association between diet and exercise and quality of life of people with asthma (Topic 3), albeit having a modest start, have been significantly increasing in recent years. By contrast, as the instruments for measuring asthma-related quality of life, to a certain extent, have become well-established and proved their validity, there has been a slight decline of research volume for Topic 4.



**Figure 3.** Changes in research topics development.

Figure 4 presents the dendrogram, in other words, the hierarchical clustering of research disciplines in quality of life of patients with asthma. The distance or dissimilarity between clusters is indicated in the horizontal axis, while the vertical axis shows the research disciplines. The red lines show the depth for the cut-off of the analysis [27]. According to Figure 4, the research landscapes in quality of life among patients with asthma are rooted in the following disciplines: (a) Health policy and services, (b) Health care sciences and services and (c) Public, Environmental and Occupational health, as the first chunk in the bottom the dendrogram. In the top part, we found the integration of: (a) Respiratory system, (b) Critical care medicine, and (c) Cardiac and Cardiovascular system.

**Figure 4.** Dendrogram of coincidence of research areas using the Web of Science (WoS) lassifications.
