The State of Dispositional Mindfulness Research

We present a bibliometric review of research on trait mindfulness published from 2003 until 2021 to determine the current state of the field and identify research trajectories. A search conducted on Aug 25, 2021, using the search terms “trait mindfulness” OR “dispositional mindfulness” in the Web of Science Core Collection identified 1405 documents. Using keyword-based network analyses, the various clusters suggested two major approaches in the field, one focusing on cognitive attentional processes, and a second approach that encompasses a wider field of well-being and clinical research topics. We also documented increasing consolidation of research fields over time, with research on wider individual differences such as personality being subsumed into clinically and well-being-oriented research topics. More recently, a distinct theme focused on the validity of measurement of mindfulness emerged. In addition to general patterns in the field, we examined the global distribution of trait mindfulness research. Research output was substantially skewed towards North American-based researchers with less international collaborations. Chinese researchers nevertheless also produced research at significant rates. Comparing the difference in research topics between China and the US-based researchers, we found substantial differences with US research emphasizing meditation and substance abuse issues, whereas researchers from China focused on methodological questions and concerns around phone addiction. Overall, our review indicates that research on trait mindfulness might profit from conceptual and cultural realignment, with greater focus on individual differences research as well as stronger focus on cross-cultural and comparative studies to complement the strong clinical and cognitive focus in the current literature.

Mindfulness is a concept that originally formed part of a wider philosophical and spiritual belief system associated with Buddhism. Core ideas inspired and derived from this Buddhist philosophy were imported into Western psychology and medical practice during the second half of the twentieth century . Mindfulness-based interventions have been widely incorporated into clinical practice (Karl et al., 2022) and have been shown to be effective in addressing a wide range of mental health issues . This ease of implementation and efficacy in addressing mental health issues prominent in Western societies (especially anxiety and depression) has led to a substantial growth in the field (Creswell, 2017;Van Dam et al., 2018).
Building on this research on mindfulness interventions, a separate body of literature has emerged that focuses on stable, trait-like individual differences in mindfulness. Trait mindfulness is generally conceptualized as "the general tendency of a person to show characteristics of nonjudgmental awareness of present-moment experience in their everyday life" (Krägeloh, 2020, p. 64). This view is reflective of the whole trait theory in personality (Fleeson, 2001;Fleeson & Jayawickreme, 2015). This theory views traits as mean descriptors of underlying density distributions of related states (for example trait extraversion is viewed as the average descriptor of extraversion states). In line with this perspective, trait mindfulness not only has been shown to be influenced by consistent mindfulness practices, but is also present in non-practitioners . Importantly, meta-analytic evidence indicates that increased trait mindfulness has a host of beneficial outcomes ranging from positive work outcomes to psychological well-being (Carpenter et al., 2019;Karyadi et al., 2014;Mesmer-Magnus et al., 2017;Sala et al., 2020). This focus on individual differences created a second and rather distinct research line in addition to clinical intervention studies, focusing on trait mindfulness that aim to identify outcomes, predictors, and underlying mechanisms of such stable interindividual differences. Research on trait mindfulness opens up new avenues to understand mindfulness from neuroscientific, biological, and individual difference perspectives, as well as providing opportunities for identifying possible cultural differences.
The last decades have been marked by a diversification and broadening of this new body of inquiry beyond the original focus of clinical interventions. A number of overviews focusing on specific topics in the field of mindfulness are available already (Baer, 2006;Chiesa et al., 2011;Keng et al., 2011). Given the diversity of the theories and approaches, researchers have started to use approaches such as bibliometry (the systematic analysis of bibliographic meta-data such as keywords and authorship) to generate overviews of the field of mindfulness (Baminiwatta & Solangaarachchi, 2021;Karl et al., 2022;Kee et al., 2019;Lee et al., 2021;Ma et al., 2021), and to identify the relationships of empirical research with Buddhist theoretical foundations (Valerio, 2016). Nevertheless, currently, no such high-level overview of the field of trait mindfulness is available. The absence of authoritative overviews of research trends makes it difficult to track the development and current state of this specific subfield. This is particularly important because the study of trait mindfulness allows building new bridges to different areas of psychology and clinical practices.
In this review, we aim to provide a systematic documentation of the trait mindfulness research field using a bibliometric approach. In the current study, we aim to advance four major goals: First, we map out the research-space around trait mindfulness and take stock of current research fields and important publications and authors, identifying broad research trends. Second, what are central themes of research across the corpus and how have they evolved over time? Third, how is research on trait mindfulness distributed globally?

Data Source
We used a broad search strategy using the Web of Science (WOS) on the 25 th of August, 2021. In order to identify the maximum possible records, we used the search strings: "Dispositional Mindful*" OR "Trait Mindful*". We initially started our search from 1970 to the present day, but found the first explicit mention of either search term in 2003. We therefore restricted the year range to 2003-2021. We downloaded all articles as bibtex files, including all available information such as keywords, abstracts, and authorship information. We combined all files into one master-database representing the full corpus and transformed the files into processable dataframes using the bibliometrix package (Aria & Cuccurullo, 2017) in R (R Core Team, 2021). All data and analysis code can be found on the OSF (https:// osf. io/ 84m95/? view_ only= a5650 11c95 9648a 2a3cd ccd54 86d10 0d).

Descriptive Analyses
We first calculated descriptive statistics based on the number of publications per year, and per publication outlet, calculated the most highly cited papers within the current corpus and the most highly cited papers within the larger literature (which includes citations by papers outside the current corpus).

Research Clusters
To provide a high-level overview over author-provided keywords, we applied multiple-correspondence analysis based on a co-occurrence matrix of stemmed author assigned keywords. Importantly, this analysis extracted clusters of keywords, representing archetypical lenses of examination of trait mindfulness; therefore, individual documents can contain keywords from multiple clusters. As this method yields exploratory results that are dependent on the included variables, we decided to implement three different cutoffs for minimal degrees of keyword associations included in the analysis. To capture the broad range of topics addressed by authors, we decided to cut at 5, 25 (shown in Fig. 2 in the supplement), and 50 minimum degrees (Fig. 1).

Thematic Evolution of Research over Time
To examine the change in the research of mindfulness, we examined the evolution of themes across the last decade of research. We split the dataset into two blocks running from 2003 to 2010 and a second block from 2011 to 2021. We extracted all publisher-provided keywords, to capture higher order themes, that occurred at least two times in the second slice of the network. Following procedures described by Callon et al. (1991) which then created thematic maps based on keyword co-occurrence matrices. After normalization, clusters within these coword matrices are calculated using the relative strength of word co-occurrences within and across different clusters, maximizing within-cluster associations (Cobo et al., 2011). These clusters are then displayed via network centrality and network density metrics. Centrality is calculated as the sum of all frequency-normalized links between any keywords within one cluster and keywords in any of the other clusters, capturing the importance of particular theme within the larger network (representing the importance within the literature within that time period). Density is calculated as the frequency-normalized strength between any two words within a cluster divided by the number of words within the same cluster. Therefore, this captures the strength of internal ties and can be interpreted as the internal development or consistency of a theme within a literature. A thematic map displays these two statistics within a two-dimensional space, providing a visual representation of the centrality and coherence of research fields. Using this graphic representation, it is possible to classify research clusters in a rather intuitive way within a four-quadrant system of (1) Niche Themes (well-developed internal ties but unimportant external ties, implying high density but low centrality); (2) Motor Themes (well developed and important for the structuring of a research field, high centrality and density); (3) Basic Themes (important for a research field but are not developed, high centrality but low density); and (4) Emerging/ Declining Themes (weakly developed and marginal, both low density and centrality).

Mindfulness Research Across Cultures
We first examined the frequency of trait mindfulness research by country, using the first/corresponding author as a point of reference for each article. We also computed the collaboration rates between all authors by country and represented these associations within a network structure.

Research Impact and Focus Comparing USand Chinese-Based Research
We focused on the two most active research regions in the Western and Eastern hemispheres (US and China, respectively). We calculated citation metrics and keyword frequencies separately for each nation as well as for a list of keywords that are common to both groups of researchers. To examine the correlation of the relative importance of keywords across countries, we transformed the frequencies within countries into rank-orders with ties broken at random (to increase the robustness, we bootstrapped the analysis 1000 times).

Descriptive Analysis of Trait Mindfulness Research
Research on individual differences in dispositional mindfulness has shown substantial increase over the last two decades ( Fig. 1 in the supplement) with an average growth rate of 31.64% per year. Overall, we found 1405 documents (1169 articles, 72, early access articles, 5 proceeding papers, 8 corrections, 5 editorials, 1 letter, 68 meeting abstracts, 9 proceeding papers, 64 reviews, 1 book chapter review, 3 early access reviews) in 495 unique sources (journals, books, etc.). Table 1 shows the 10 most common sources, which unsurprisingly were headed by the journal Mindfulness. Importantly, the second most important outlet for trait mindfulness research is Personality and Individual Differences. Most articles were authored by multiple authors with an average of 2.79 authors per document. To examine important papers cited by studies included in our corpus in the global citation network (all articles available on the WoS) and our slice of the citation network (studies within our corpus of articles), we extracted the ten most important papers based on their global and local citation scores. We found a substantial correlation of number of citations of a document within our network with its overall citations (indicating that our network captures a representative slice of the overall citation network; r = 0.96, p < 0.001). At the same time, when using rank correlations, the relative order changed which indicates differential importance of papers in our network compared to their importance in the general field (r = 0.43, p < 0.001). Focusing on specific features, the ten most important papers in the general citation network focused largely on scale development and conceptual definitions (Table 2) and were exclusively written by North American-based first authors. In contrast, papers in our local network focused largely on clinically relevant outcomes, such as well-being or psychological issues. To clarify the concepts researched jointly with dispositional mindfulness, we extracted the twenty most common keywords applied by authors to their articles in our corpus (Table 3). This revealed a similar picture to the most cited articles, with clinically relevant such as stress, anxiety, and depression being central research foci.

Identifying Research Themes and Trends
Cutting at a minimum of 5 degrees, we found a split in the keywords separating out clusters of general research on trait mindfulness, focusing on topics such as anxiety and depression and a cluster that focused on MBSR research. Cutting at 25 degrees, we found four clusters. A first cluster split from the main cluster of trait mindfulness and specifically included research on depression and stress. Two other clusters emerged: one focusing on emotion regulation, and a final cluster capturing labelling of mindfulness as either dispositional or trait. Finally, cutting at 50 degrees, three clusters were present. One clusters focused on mindfulness, mediation, and emotion regulation. The two other clusters remaining identical to the stress, anxiety, depression cluster, and the labelling of mindfulness cluster found for the 25 degree solution.

Temporal Changes in Trait Mindfulness Research
In the network structure covering 2003-2010 (we show all themes in Table 4 and in Fig. 2a, b), we found three niche themes: (1) reduction (key terms: reduction, generalized anxiety disorder; focusing on reducing general anxiety disorder); (2) personality (key terms: personality, consciousness, model, esteem; focusing on individual differences and self-esteem); and (3) the 5-factor model (key terms: 5-factor model, information, negative affect; focusing on specific avenues of information processing, this theme bordered on being a motor theme). A theme labelled "self-report" (key terms: self-report, awareness, meta-analysis, validation, amygdala, attention, dispositional mindfulness, prefrontal cortex, responses, scale; focusing on cognitive validations of self-report) bordered both motor themes and basic themes.
Overall, we found that the nodes with the highest strength were the USA (186), the UK (87), China (80), Netherland (52), and Australia (44), indicating that most cross-country collaborations included authors from these countries.

Cross-cultural Comparison of the Most Active Countries per Region: USA vs China
As China was the only non-American/non-European country among the top 10 countries, we compared the keywords applied by authors in China to keywords applied by US authors. Overall, we found 144 overlapping keywords, representing 9.375% of total words in the combined country set (N = 1536). Using only keywords that were present in both samples, we found a high correlation in usage frequency: r(144) = 0.93, p < 0.001. In contrast, we found a lower correlation between ranks for terms with a usage greater than 1 across countries: r(40) = 0.505[0.501, 0.509], p < 0.003[0.002, 0.003]. This indicates there are several terms that are shared across countries, while each country also use unique terms.
Comparing the most frequently used keywords in the USA and China (see Table 3), we find similar patterns with sample descriptors and specific indicators of ill-being such as Anxiety and Depression, and Substance Abuse taking a higher place in the USA. The potentially most striking difference is (1) the absence of Meditation in the Chinese sub-network, which ranks relatively highly in the USA network and (2) the strong presence of statistical features such as Mediation in Chinese articles. We examined the country differences further by examining the twenty most cited  Table 6 (we also list the top cited papers in the Chinese corpus in Table 7, indicating which papers by China-based first authors had the largest impact on the field). Overall, we found an overlap of 60% in the top cited documents, suggesting that research in both countries draws on somewhat similar sources. Documents which appeared among the most cited papers in China but   (Deng et al., 2012), methodological and statistical questions (A. F. Hayes, 2013;Hu & Bentler, 1999;Podsakoff et al., 2003), wellbeing (Coffey & Hartman, 2008;Weinstein et al., 2009), resilience to trauma (Thompson et al., 2011), social anxiety (Goldin & Gross, 2010), and mindfulness theory (Garland et al., 2015). Documents which appeared among the most cited papers in the USA but not China were focused on mindfulness scale development (Baer et al., 2004), cognitive neuroscience Creswell et al., 2007), mechanisms of meditation (Hölzel et al., 2011), romantic relationships (Barnes et al., 2007), well-being (Grossman et al., 2004;Kabat-Zinn, 1982), measurement of stress (Cohen et al., 1983), and emotion regulation (Feldman et al., 2007). Furthermore, we examined the top five cited articles that were not shared between the countries for each country.

Discussion
Our current study aimed to provide a mapping of the research spaces investigating trait mindfulness. A few findings stand out, leading to two important considerations about the current research on trait mindfulness: one being the unequal distribution of mindfulness research globally and possible implications for our understanding of trait mindfulness, the other is the focus on clinical and health outcomes.

Global Distribution of Mindfulness Research
First, resembling psychology as a wider field (Henrich, 2020), we found a dominance of US and European researchers in the field of mindfulness. Especially US-based first authors showed a low likelihood to collaborate with other colleagues internationally. If they did, they enjoyed a high centrality in the collaborators network, indicating that a substantial body of work on mindfulness is exclusively focused on US samples. The high collaboration statistics also suggest that research on trait mindfulness in other countries often included US perspectives. Given the historical origin of mindfulness as a Buddhist philosophical construct, this finding of Western researchers and perspectives raises questions and possible challenges about the current conceptualization and authenticity, from a Buddhist perspective, of the construct of mindfulness, which already has received some discussion (Grossman & Dam, 2011). An encouraging trend is that this is being recognized as seen by the central position of this paper in studies being published by USbased authors. Furthermore, there is increasing awareness that individual difference measures aimed at capturing trait mindfulness such as the FFMQ may perform sub-optimally in non-WEIRD (Western, educated, industrialized, rich, and democratic) populations (Christopher et al., 2009;Karl et al., 2020), which in turn has led to the development of alternative and more culturally aligned measures by researchers (Ng & Wang, 2021). If research on trait mindfulness fails to incorporate more diverse non-WEIRD perspectives, this might not only result in operational definitions of trait mindfulness that are not universally accessible, but also may fail to meet the different needs of populations around the globe. This becomes apparent looking at the different use of keywords in the two biggest producers of research, one based in the Global West (USA) and the other based in the Global East (China). In both countries, researchers focused on well-being outcomes, yet the relative priority was markedly different. Whereas in the USA substance abuse was a major target of research (potentially as a reaction to the ongoing Opioid epidemic in the United States; Manchikanti et al., 2012), this was absent in China when examining the major research trends as indicated by keywords. Interestingly, a range of papers that were highly cited in China compared to the US focused on phone addiction, which has been a substantial topic of both societal concern and research in the Chinese context (Li & Lin, 2019;Ni et al., 2009). Taken together, this showcases how trait mindfulness is shaped by the needs of individual cultures and highlights the need to carefully consider the research context of current trait mindfulness studies.
Furthermore, while the keyword "meditation" was a central research topic connected to trait mindfulness in the USA, it was again absent in China. It might be that the term "meditation" has different, possibly more spiritual or religious connotations and therefore it is not used by authors within Chinese research institutes (for a special issue on cultural conceptualizations of mindfulness see; Kirmayer, 2015). Interestingly, a common term in both countries was Mediation, indicating that a substantial portion of research on trait mindfulness does not research direct relationships, but rather tests more complex path models (for the most highly cited examples in the current set see: Demarzo et al., 2014;Iani et al., 2017;Nitzan-Assayag et al., 2015). When examining the unique high impact citations driving research in China and the USA, we found a reflection of this pattern with a substantial number of references in the USA focusing on meditation or mindfulness practice (Carmody & Baer, 2008;Grossman et al., 2004;Hölzel et al., 2011), whereas uniquely important references in China focused on methodological concerns (Deng et al., 2012;A. F. Hayes, 2013;Hu & Bentler, 1999;Podsakoff et al., 2003). Interestingly, we also found that the top three key terms in China were labels of mindfulness (mindfulness, trait mindfulness, dispositional mindfulness), whereas in the USA authors seem to elaborate less on the label mindfulness and specific terms (trait or dispositional mindfulness) are of lower importance compared to outcome-focused keywords.
Second, while examining key terms and their development, we found an increasing consolidation of trait mindfulness research into distinct clusters and a strong focus on outcomes compared to predictors. Examining the thematic maps of overall keywords related to trait mindfulness, we found that a major split in the research field exists between research focusing on MBSRs and basic cognitive processes, and a more diverse field containing personality and positive psychology. Narrowing down further this central cluster separated into three clusters, the emergent clusters captured different clinical approaches centred around adolescents, general research on emotion regulation, and a cluster specifically focused on anxiety, stress, and depression. Overall, breaking apart the keywords used in conjunction with trait mindfulness reveals that the field is mostly split into cognitive research and outcome-focused clinical research.
Zooming out to the broader trends in the literature, the result of the keyword analysis is mirrored in the development of the themes overall across the time period. Overall, research on mindfulness has consolidated into distinct subfields over the last two decades. Research topics such as personality and individual differences, over time, became less of a separate focus and merged with the wider literature on stress reduction. This might represent an increasing focus of research on clinically relevant outcomes with mechanism and individual differences subsumed under these topics. Interestingly, a distinct subfield has emerged that focused on psychometric approaches to mindfulness, indicating the increasing emphasis in the field to consolidate and validate measurements of mindfulness (Andrei et al., 2016;Karl & Fischer, 2020;Karl et al., 2020;Siegling & Petrides, 2014. In contrast, the thematic maps show an emergence of new clusters that focus on specific subtopics such as LGBTQIA + related topics and topics surrounding romantic relationships. Overall, research on trait mindfulness has consolidated around psychometric issues and outcome-focused topics such as stress, well-being, and clinical interventions. This reveals a potential imbalance within the field, with increasing focus on outcomes, while less research is conducted on potential predictors of mindfulness. To achieve a fuller understanding of dispositional mindfulness, it is essential to address potential predictors given the complex causal interplay between mindfulness and established individual differences such as personality  and situational variables such as affect Mahlo & Windsor, 2021).

Limitations and Future Research
One major limitation of our current work lies in the database (Web of Science) used. Our current source might miss papers that are not indicated in the WoS or not formally published (so-called grey literature). Our search also relied on author (or publisher) assigned key terms to identify articles of interest. Furthermore, while the bibliometric approach we utilised allows us to describe the relationship between keywords that are present in the corpus, it cannot provide information about keywords that are not present and can also not provide information on which keywords from the nomological network are absent. Additionally, our use of English language search terms leave open the question how terms used in other languages map onto our selected key terms.
Last, given the substantial body of literature resulting from our search, we focus on broad trends that do not allow for a narrative review or the identification of more qualitative and nuanced trends of the research field. We provide our full database on the Open Science Framework to allow interested researchers to explore more narrow sub-topics.
Utilizing a bibliometric approach to provide a high-level perspective, our research indicates that the field of trait mindfulness is maturing and quite distinct areas focusing on cognitive attentional processes and clinical interventions have emerged, with a strong focus of the field on outcomes of mindfulness, including both applied and in basic attentional processes. In contrast, potential predictors of trait mindfulness, such as cultural and individual differences, are less developed in recent thematic networks. The increasing interest in measurement and validity of current mindfulness constructs (manifested in the emergent themes around scale validity) might present an opportunity to more closely examine the nomological network of mindfulness and individual differences, as well as cultural differences in mindfulness.
Author Contribution JAK: designed and executed the study, conducted the data analyses, and wrote the paper. RF: collaborated with the design, writing of the study, and analysis of the data.
The authors do not have any potential conflicts of interest and no ethical approval was necessary for the use of published materials.

Funding Open Access funding enabled and organized by CAUL and its Member Institutions
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