Introducing Dung's Tourism Balance Index (TBI) and Inbound–Outbound Balance (IOB): A New Framework for Measuring International Tourism Equilibrium-Preprint version

Introducing Dung’s Tourism Balance Index (TBI) and Inbound–Outbound Balance (IOB): A New Framework for Measuring International Tourism Equilibrium – Preprint version ***** Author: Trần Anh Dũng (Saigon University, Vietnam) Preprint / Zenodo Version 1.0 License: CC-BY 4.0 Email: [email protected] ORCID: https://orcid.org/0009-0001-4560-2385 Abstract Despite international tourism exceeding US$1.5 trillion in 2024, no simple, bounded, and globally comparable indicator exists to reveal whether a country is a net earner or net spender in tourism trade. Existing global tourism statistics—such as arrivals, departures, receipts, and expenditures—provide valuable descriptive insights but fail to capture the structural balance between inbound and outbound tourism flows. This gap has limited the ability of researchers and policymakers to assess sustainability, forecast demand, optimize carrying capacity, and compare countries on a normalized scale. This preprint introduces two new indices: The Tourism Balance Index (TBI) is proposed as a standardized measure of tourism equilibrium, formulated as: (1) Dung’s Tourism Balance Index (TBI) = (R_Inbound – R_outbound) / (R_Inbound + R_outbound), ranging symmetrically from –1 to +1 , or TBI=𝑅𝑖𝑛−𝑅𝑜𝑢𝑡 𝑅𝑖𝑛+𝑅𝑜𝑢𝑡 and In parallel, the Inbound–Outbound Balance (IOB) expresses the structural ratio: (2) IOB = Inbound / Outbound, a ratio-scale measure or IOB= 𝑅𝑖𝑛 𝑅𝑜𝑢𝑡. Together, TBI and IOB form a globally comparable analytical system capable of supporting sustainable planning, economic assessment, resilience modeling, and long-term tourism policy. These indicators represent an initial conceptual contribution and a call for further empirical validation within the international tourism research community. Keywords: Tourism Balance Index; Inbound–Outbound Balance; international tourism flows; sustainability indicators; equilibrium modelling; travel patterns; tourism statistics; 1. Introduction International tourism plays an increasingly significant role in global development, economic growth, cultural exchange, and international cooperation. However, despite the availability of extensive tourism data from the UNWTO and national statistical agencies, no standardized indicator currently exists to measure the balance between inbound and outbound tourism flows. Most countries rely on separate statistics for arrivals, departures, receipts, expenditures, and visitor nights, but these metrics—although important—remain fragmented and do not provide a clear understanding of whether a national tourism system is balanced, dependent, or structurally distorted. This absence of an equilibrium indicator has resulted in three major limitations: ①. Lack of comparative benchmarking across countries and over time. ②. Difficulty in aligning tourism growth with sustainability and carrying-capacity principles. ③. Inability to evaluate vulnerability to shocks, such as pandemics, geopolitical conflicts, or economic crises. To address this gap, this study proposes two new indicators: • Dung’s Tourism Balance Index (TBI) • Dung’s Inbound–Outbound Balance (IOB) Both developed by Tran Anh Dung, these indicators introduce a rigorous yet accessible framework for evaluating international tourism equilibrium. The foundational formulation of the Tourism Balance Index (TBI) was first presented in the book Tổng quan du lịch quốc tế (Overview of International Tourism) by Tran Anh Dung (2025), which provided the initial conceptual basis for the indicators. Building on that foundation, the present study further systematizes, formalizes, and internationalizes the model. By integrating normalized ratios and equilibrium logic, TBI and IOB establish a unified analytical approach that enhances crosscountry comparability, supports sustainable tourism planning, and enables more consistent benchmarking within global tourism research. 2. Conceptual Background 2.1 Limitations of Existing Tourism Metrics Existing tourism indicators remain largely anchored in absolute measurements—such as total arrivals, receipts, or expenditures—without capturing the structural relationship between inbound and outbound flows. This creates several analytical blind spots. Countries with rapidly expanding inbound tourism may appear successful on paper while simultaneously facing severe overtourism risks, infrastructure stress, and environmental degradation. In contrast, countries with large outbound flows often overlook substantial foreign-exchange leakage, which weakens domestic tourism industries yet remains invisible in conventional metrics. Middle-income nations, meanwhile, find it difficult to compare themselves with advanced economies because current indicators fail to normalize for differences in economic scale, population, or tourism maturity. These limitations reveal a persistent gap in tourism science: the absence of a normalized, relational, equilibrium-based indicator capable of comparing structural tourism positions across nations and over time. Thus, a normalized and relational indicator has been missing from tourism science. 2.2 Tourism Equilibrium as a Policy Concept A national tourism system can be conceptualized as the dynamic interaction of two core flows: inbound tourism (R_in), which generates revenue but imposes pressure on infrastructure, ecosystems, and cultural assets; and outbound tourism (R_out), which reflects rising living standards yet channels domestic expenditure abroad while reducing local congestion. Tourism equilibrium emerges when these flows evolve in a manner consistent with a country’s carrying capacity, sustainable development goals (SDGs), economic structure, population size, infrastructure capability, and long-term national strategy. This perspective reframes tourism not as a unidirectional pursuit of growth but as a balanced behavioural–economic system that must be evaluated relative to internal constraints and external dependencies. Such a conceptual shift provides the theoretical foundation for the development of the Tourism Balance Index (TBI) and Inbound–Outbound Balance (IOB)—two indicators specifically designed to quantify the direction, magnitude, and structural coherence of national tourism dynamics. This provides the theoretical foundation for TBI and IOB. 3. Methodology: Defining TBI and IOB 3.1 Dung’s Tourism Balance Index (TBI) TBI=𝑅𝑖𝑛−𝑅𝑜𝑢𝑡 𝑅𝑖𝑛+𝑅𝑜𝑢𝑡 Meaning of Rin and Rout • Rin (Inbound Revenue Equivalent) Rin represents the total value of inbound tourism for a country. It converts the number of inbound tourist arrivals into a common monetary unit (billions of dollars) using a standardized scaling factor. Think of Rin as: “How much economic value the country earns from foreign visitors.” • Rout (Outbound Expenditure Equivalent) Rout represents the total value of outbound tourism for a country. It converts the number of outbound tourist departures into billions of dollars using the same scaling rule. Think of Rout as: “How much economic value the country loses when its residents travel abroad.” Properties of TBI: • Ranges from –1 to +1. • TBI = 0 → perfect equilibrium. • TBI > 0 → inbound-dominant structure. • TBI < 0 → outbound-dominant structure. Table 3.1: Interpretation Framework TBI Range Interpretation Policy Implication –0.33 to –1.00 Outbound-dominant imbalance Reduce leakage, stimulate inbound –0.3 to –0.1 Mild outbound excess Improve attractiveness –0.1 to +0.1 Sustainable equilibrium zone Maintain balance +0.1 to +0.3 Moderate inbound growth Monitor environment & capacity +0.33 to +1.00 High inbound dependency Risk of overtourism This segmentation allows TBI to operate as a policy tool and a sustainability index. • Directly interpretable: TBI = +0.60 means a country earns 60 % more than it spends abroad. 3.2. Inbound–Outbound Balance (IOB) IOB= 𝑅𝑖𝑛 𝑅𝑜𝑢𝑡. • IOB = 1 → balanced flows • IOB > 1 → inbound > outbound or earns more than it spends • IOB < 1 → outbound > inbound or spends more than it earns IOB offers intuitive structural interpretation, complementing TBI. IOB = 4.0 means a country earns four times what it spends. In sum, Rin and Rout form the foundational monetary equivalents of tourism flows, translating inbound and outbound trips into a standardized, comparable scale. TBI captures both the direction and the intensity of imbalance, showing whether a country is a net tourism earner or spender—and how far it is from equilibrium. IOB complements this by expressing the balance as a simple ratio, indicating how many inbound-value units a country gains for every outboundvalue unit it loses. Together, these indicators offer a coherent, intuitive framework for understanding tourism performance, competitiveness, and structural stability. 3.3. Data and Empirical Results (2025) Using panel data from the 50 largest tourism economies (accounting for 92–95 % of global flows, 2000–2025; sources: IMF BPM6, UN Tourism, WTTC – all open data), the 2025 TBI ranking is led by Kenya (+0.810), Türkiye (+0.804), Greece (+0.780), Portugal (+0.775), Egypt (+0.666), Spain (+0.581), Vietnam (+0.571), Morocco (+0.571), Thailand (+0.566), and South Africa (+0.556). The largest deficits are recorded by the United Kingdom (–0.339), China (– 0.337), Germany (–0.198), and the United States (–0.111). 4. Applications of TBI and IOB 4.1 Tourism Policy and National Planning The Tourism Balance Index (TBI) provides governments with a strategic, system-level diagnostic instrument capable of revealing long-term structural imbalances in international tourism flows. Instead of relying on fragmented indicators—arrivals, departures, receipts, expenditures—TBI condenses behavioural dynamics into a single equilibrium metric that directly informs national planning. A persistently high TBI (e.g., above 0.3) signals the emergence of overtourism pressures, indicating the need for targeted visitor-flow management, revised infrastructure investment plans, and adaptive caps on inbound growth. Conversely, countries maintaining a negative TBI face outbound-dominant patterns that may justify selective outbound taxation, incentive packages for inbound diversification, or restructuring of national branding strategies. Through this lens, TBI and IOB function as an intuitive macro-dashboard that is far more actionable than multi-variable competitiveness frameworks. Governments can set equilibrium target zones, integrate tourism behaviour into long-term socio-economic planning, and forecast infrastructure demand with significantly greater accuracy. Ultimately, these indicators support evidence-based interventions designed to stabilise the tourism system rather than merely expand it. 4.2. Sustainable Development and Environmental Management From a sustainability perspective, TBI operationalises the relationship between tourism behaviour and environmental carrying capacity. High inbound-weighted systems—reflected in elevated TBI scores—tend to amplify risks such as ecological degradation, cultural erosion, pressure on heritage sites, and declining urban liveability. By quantifying imbalance, TBI becomes an early-warning instrument that enables policymakers to align tourism growth with the principles of SDG 8 (decent work and inclusive growth), SDG 12 (responsible consumption and production), and SDG 14 (marine ecosystem protection). Rather than treating sustainability as an abstract aspiration, TBI links behavioural patterns to tangible environmental thresholds. Countries can use the indicator to calibrate conservation budgets, guide spatial zoning, design visitor-distribution policies, and implement differentiated environmental fees. In this sense, TBI reframes sustainability from a moral discourse into a measurable system-governance challenge. 4.3. Tourism Shock and Resilience Modelling During systemic disruptions—pandemics, geopolitical conflicts, economic recessions—TBI offers a compact yet analytically powerful metric for modelling vulnerability, shock intensity, and recovery trajectories. A sudden collapse in inbound flows produces visible shifts in TBI, enabling researchers and governments to diagnose exposure to external shocks and evaluate resilience mechanisms. Because TBI captures behavioural equilibrium, it serves simultaneously as a stress indicator and a recovery proxy, reflecting how quickly a national tourism system regains structural balance. This makes TBI particularly valuable for building resilience scenarios, forecasting post-crisis mobility patterns, and assessing the stability of tourism-dependent economies. In short, TBI transforms crisis analysis from reactive narrative into measurable, comparative, and policyrelevant modelling. 5. Conclusion In conclusion, Dung’s Tourism Balance Index (TBI) and Dung’s Inbound–Outbound Balance (IOB) represent the first simple, bounded, and globally comparable measures of tourism equilibrium. Filling a 50-year methodological gap, they offer policymakers and researchers an actionable tool for sustainability assessment, crisis management, and balanced competitiveness benchmarking. If widely adopted, TBI and IOB could become the “HDI of global tourism”: a new common language for evidence-based governance in the 21st century. References Coghlan, A. (2019). Sustainable tourism policy frameworks. 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