We study large deviations for Cox–Ingersoll–Ross processes with small noise and state-dependent fast switching via associated Hamilton–Jacobi–Bellman equations. As time scales separate, when the noise goes to 0 and the rate of switching goes to $\infty$, we get a limit equation characterized by the averaging principle. Moreover, we prove the large deviation principle with an action-integral form rate function to describe the asymptotic behavior of such systems. The new ingredient is establishing the comparison principle in the singular context. The proof is carried out using the nonlinear semigroup method from Feng and Kurtz’s book [14].

The vast majority of researchers, actuaries, and demographers use standard time series analysis techniques to project time-varying parameters of popular mortality forecasting methods such as the Lee–Carter and Li–Lee models. However, spatial dependence can be as significant as temporal autocorrelation in these time series, and the underlying panel structure of the data is often neglected. We draw on techniques from panel and spatial econometrics, including ordinary and spatial dynamic panel linear models, spatiotemporal autoregressive integrated moving average processes, and spatial eigenvector filters, to capture such dependence and improve projections. We present a methodology to estimate the parameters of these techniques from spatial multipopulation mortality series, select their optimal hyperparameters, and use them for forecasting. We propose a tailor-made robust selection framework to identify the best model–technique combinations for each country, as well as a bootstrap-based procedure to quantify projection uncertainty with accurate nominal coverage on a separate validation period and a strategy for assessing the quality of the resulting prediction intervals. We test these methods on mortality data from 22 European countries. The results show that the proposed techniques yield a clear advantage in both point and interval forecasts for several populations, and these findings are corroborated by a robust selection design and additional robustness checks. These improvements have the potential to deliver meaningful gains for life insurance, pensions, and other contexts involving longevity risk.

This retrospective study analysed 14,625 isolates of the six major hospital-associated ‘ESKAPE’ pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) collected between 2002 and 2024 in a Hungarian tertiary-care centre. Antimicrobial resistance was assessed using the antibiotic resistance index (ARI), multidrug resistance (MDR) ratios, and resistance instability index (RII). A. baumannii and E. faecium showed the highest resistance burdens and instability. Age showed a significant monotonic association with resistance (Spearman r = 0.88), with peaks in infants, middle-aged women, and the elderly. Species-specific age trends varied, with a negative correlation seen in Enterobacter spp. Hierarchical clustering grouped pathogens by resistance trajectory rather than taxonomy. Pairwise resistance distances confirmed divergence between Gram-positive and Gram-negative species. Resistance to aminoglycosides and sulphonamides showed the highest year-to-year variability, as quantified by the RII, particularly in A. baumannii and E. faecium. Vector autoregressive (VAR) modelling predicted continued MDR increases in these species. A strong correlation was found between ARI and RII (Pearson r = 0.85, p = 0.032). These findings underscore the importance of integrating resistance magnitude and volatility in surveillance.

We consider the problem of maximizing the expected average reward obtained over an infinite time horizon by n weakly coupled Markov decision processes. Our setup is a substantial generalization of the multi-armed restless bandit problem that allows for multiple actions and constraints. We establish a connection with a deterministic and continuous-variable control problem where the objective is to maximize the average reward derived from an occupancy measure that represents the empirical distribution of the processes when $n \to \infty$. We show that a solution of this fluid problem can be used to construct policies for the weakly coupled processes that achieve the maximum expected average reward as $n \to \infty$, and we give sufficient conditions for the existence of solutions. Under certain assumptions on the constraints, we prove that these conditions are automatically satisfied if the unconstrained single-process problem admits a suitable unichain and aperiodic policy. In particular, the assumptions include multi-armed restless bandits and a broad class of problems with multiple actions and inequality constraints. Also, the policies can be constructed in an explicit way in these cases. Our theoretical results are complemented by several concrete examples and numerical experiments, which include multichain setups that are covered by the theoretical results.

The InsurTech industry has undergone almost a decade of development. Despite its initial success, the industry now faces challenges from global uncertainties and regulatory adjustments, which lead to concerns about sustainable profit growth and the ongoing development of InsurTech. This study provides an overview of the evolution of InsurTech development from both academic and practical perspectives. A bibliometric analysis of more than 20,000 published articles, including both practice articles and academic articles, is put forward. As compared to other review articles in this field, which often focus on either the practice or the scholarly side of development, this article brings together a review of both academic and practice-based articles from fields relevant to InsurTech including artificial intelligence, the Internet of Things, and also powerful computing technology. A keyword extraction framework is developed and applied. Using text analysis, this study reviews the prioritized topics, analyzes the robustness of the development of publication growth, identifies emerging insurance business lines, and also highlights the challenges and gaps in both academic and practice development. This study aims to motivate collaboration between academics and industry to face the challenges posed by the integration of InsurTech into insurance operations.

We evaluate the performance and level of intergenerational cross-subsidy in flat-accrual and dynamic-accrual collective defined contribution (CDC) schemes, which have been designed to be compatible with UK legislation. In the flat-accrual scheme, all members accrue the benefits at the same rate, irrespective of age. This captures the most significant feature of the Royal Mail Collective Pension Plan, which is currently the only UK CDC scheme. The dynamic-accrual schemes seek to reduce intergenerational cross-subsidies by varying the rate of benefit-accrual schemes in accordance with the age of members and the current funding level. We find that these CDC schemes can often be successful in smoothing pension outcomes postretirement while outperforming a defined contribution scheme followed by annuity purchase at the point of retirement. However, this out-performance is not guaranteed in a flat-accrual scheme, and there is little smoothing of projected pension outcomes before retirement. There are significant intergenerational cross-subsidies in the flat-accrual scheme, which qualitatively mirror the cross-subsidies seen in defined benefit schemes, but the magnitude of cross-subsidies is much larger in flat-accrual CDC schemes. The dynamic-accrual scheme design seeks to reduce such cross-subsidies, but we find significant cross-subsidies still arise due to the approximate pricing methodology used to determine the benefits.

We assessed the association between voluntary polymerase chain reaction testing of travellers and reported infection rates in the Ogasawara Islands compared with those in several other Tokyo islands. The implementation of polymerase chain reaction testing over a 2-year period was evaluated. Between September 2020 and September 2022, 38,943 of 45,900 travellers to the Ogasawara Islands underwent pre-travel polymerase chain reaction testing, with a notable increase in uptake during states of emergency. Ogasawara reported 385 positive coronavirus disease 2019 cases, with no hospitalizations or severe cases among residents, in contrast to the higher infection and hospitalization rates in Tokyo. Pre-boarding polymerase chain reaction tests were associated with lower reported infection rates in this island setting. These findings suggest that combining pre-travel testing with local mitigation measures, including case isolation systems, may help safeguard the communities of small, geographically isolated islands. These results may inform public health preparedness and response strategies for future infectious disease outbreaks.

This retrospective, cross-sectional study assessed the burden of HIV in Israel’s Maccabi Healthcare Services in 2022. Among 2.6 million individuals assessed (lookback period: > 2 decades), 1973 PWH were identified and age-sex-matched (1:5) to 9,865 randomly selected controls without HIV. We compared sociodemographic, clinical characteristics, and healthcare resource utilization (HRU; Jan–Dec 2022) between people with and without HIV and characterized antiretroviral therapy (ART) treatment patterns among PWH (Jan–Dec 2022). Compared to controls, PWH had a higher lifetime prevalence (since 1988; P < 0.001) of several comorbid conditions, including liver disease, chronic kidney disease, any cancer, and hepatitis B and C infections. Additionally, PWH had a higher rate of anxiety and depression (26.2% vs. 13.5%; P < 0.001). PWH showed higher annual HRU than controls, including ~2-fold higher hospitalizations (≥1 new admissions; P < 0.001) and frequent use of emergency, urgent, primary, specialist, and nursing care (P < 0.05). Among 1907 PWH with ≥1 ART prescription, 78.1% had ≥90% coverage in 2022, although 69.1% experienced ART interruption and 7.2% discontinuation, the latter associated with mental health issues. This study recognizes critical gaps in care that could inform strategies to improve clinical outcomes and resource allocation in health systems for PWH.

To estimate illness incidence or prevalence from wastewater data, modelling approaches may benefit from incorporating faecal shedding parameters. We systematically searched PubMed and a public repository on shedding data and included 33 studies that met at least one of our objectives. Among 32 studies, the proportion of SARS-CoV-2-infected individuals with detectable virus in stool ranged from 18 to 100%, with a pooled estimate of 54% (95% CI: 52–56%). Stratification by four clinical severity categories, ranging from asymptomatic to critically ill, showed no significant differences among categories (p-value = 0.49). The proportion of individuals with detectable SARS-CoV-2 RNA in stool was higher in children (61%) than in adults (53%; p-value = 0.02). In half of the individuals who initially shed the virus in stool, it remained detectable for an estimated 22 days post-symptom onset. Three studies documented viral load kinetics, indicating a peak between days 3 and 9. Twenty-five studies reported maximum shedding durations ranging from 2 to 12 weeks. Our review summarizes the frequency, dynamics, and duration of SARS-CoV-2 shedding in stool and may serve as a valuable foundation for modelling efforts involving faecal shedding indicators.

This paper introduces a novel expectation-maximization (EM) algorithm for estimating general phase-type (PH) distributions from left-truncated and right-censored (LTRC) data, a common challenge in survival analysis. The proposed algorithm is highly efficient with computational complexity that scales with the number of nonzero elements in the generator matrix. This feature makes the estimation of high-dimensional, sparse PH models computationally tractable and enables the practical use of the computationally intensive extended information criterion for model selection. Numerical experiments demonstrate its significant speed advantage over a modern benchmark and the applicability of PH models to complex lifetime data.

In many insurance contexts, dependence between risks of a portfolio may arise from their frequencies. We investigate a dependent risk model in which we assume the vector of count variables to be a tree-structured Markov random field with Poisson marginals. The tree structure translates into a wide variety of dependence schemes. We study the global risk of the portfolio and the risk allocation to all its constituents. We provide asymptotic results for portfolios defined on infinitely growing trees. To illustrate its flexibility and computational scalability to higher dimensions, we calibrate the risk model on real-world extreme rainfall data and perform a risk analysis.

Immunization is critical for reducing vaccine-preventable disease morbidity and mortality, yet coverage disparities persist in low-resource settings. This mixed-methods study describes characteristics of childhood immunization defaulters and explores barriers to vaccine adherence in Khyber Pakhtunkhwa, Pakistan. We recruited 380 caregivers from three tehsils in District Kohat of Khyber Pakhtunkhwa from February to July 2023, whose children under 2 years had not completed the Expanded Program on Immunization (EPI)-recommended schedule. Quantitative data from validated questionnaires and immunization cards underwent descriptive and regression analyses; qualitative interviews explored non-adherence reasons. Most respondents were fathers (96.05%); 41.84% resided in rural areas. Initial coverage was high for BCG (97.89%) and OPV0 (100%) but declined for Penta3 (26.05%) and Measles2 (4.21%). Most children (73.95%) were under 4 months. Rural defaulters were more prevalent than urban (41.84% vs. 34.47%, p < 0.001), and 89.47% had mothers with ≤high school education. While 95.26% had heard of vaccines, only 49.47% knew the EPI starting age. Defaulters with higher knowledge progressed further through the schedule (AOR: 4.55, p = 0.05). Qualitative themes included poor healthcare access, cultural norms, religious misconceptions, and migration disruptions. Interventions addressing maternal education, rural access, and knowledge gaps are essential to reduce immunization default.

When undertaking a community intervention, interventionists frequently recruit the help of community members who serve as key opinion leaders (KOLs). However, selecting a team of KOLs can be challenging because the evaluation of potential teams must balance considerations of members’ availability and diversity, as well as the team’s breadth of network coverage and cost of recruitment. This paper has two goals: to review the practical challenges that arise in the selection of KOLs for community interventions, and to facilitate the selection of KOLs when some of these practical challenges are present by introducing and demonstrating the KOLaide R package. We conclude by discussing future directions for facilitating the selection of KOLs in community intervention contexts.

We propose a novel approach to numerically approximate McKean–Vlasov stochastic differential equations (MV-SDEs) using stochastic gradient descent (SGD) while avoiding the use of interacting particle systems (IPSs) and the associated simulation costs required to achieve the ‘propagation of chaos’ limit. The SGD technique is deployed to solve a Euclidean minimization problem, obtained by first representing the MV-SDE as a minimization problem over the set of continuous functions of time, and then approximating the domain with a finite-dimensional sub-space. Convergence is established by proving certain intermediate stability and moment estimates of the relevant stochastic processes, including the tangent processes. Numerical experiments illustrate the competitive performance of our SGD-based method compared with the IPS benchmarks. This work offers a theoretical foundation for using the SGD method in the context of numerical approximation of MV-SDEs, and provides analytical tools to study its stability and convergence.

We consider a Lévy process reflected at the origin with additional independent and identically distributed collapses that occur at Poisson epochs, where a collapse is a jump downward to a state which is a random fraction of the state just before the jump. We first study the general case, then specialize to the case where the Lévy process is spectrally positive, and, finally, we specialize further to the two cases where the Lévy process is a Brownian motion and a compound Poisson process with exponential jumps minus a linear slope.

Point clouds derived from UAV photogrammetry are a cost-effective alternative to LiDAR for infrastructure inspections, but they often include both structural and non-structural elements that complicate analysis. Traditional denoising filters remove outliers indiscriminately and frequently erode edges, making it difficult to preserve the curved tunnel lining while distinguishing bolts, access gates, or pipelines. In contrast, segmentation-based approaches leverage geometric context to explicitly separate lining surfaces from ancillary components, thereby enabling more accurate deformation analysis and structural assessment. To that end, this paper presents a novel approach for denoising image point clouds using a synthetic training dataset to address the scarcity of labeled public data for enhancing point cloud quality. Unlike other denoising approaches that rely on projections or assume points lie on a predefined surface shape, this segmentation-based denoising method retains only meaningful points in their original locations, allowing for more accurate analysis of deformation. Enhanced by synthetic training datasets, the application of the proposed denoising method to a road tunnel image point cloud and a subway tunnel terrestrial laser scanning point cloud demonstrates its potential to enhance point cloud quality in tunnels with diverse geometries and point cloud data resources, even when data are limited. The method achieves an 80% mean intersection over union for both the road tunnel and the subway tunnel from manual annotation. This enables an improvement in structural deformation analysis at the mm level.

This paper develops a unified framework for catastrophe (CAT) bond pricing that integrates distortion operator theory with recurrent neural network (RNN) estimation. A novel peer-adjusted distortion factor is introduced, constructed from both the Wang transform and the jump-diffusion (JD) distortion operator, and calibrated using the market-weighted spread of comparable CAT bonds together with the target bond’s expected loss. This factor embeds prevailing investor sentiment, reinsurance capacity, and market liquidity into the distortion measure, enabling consistent pricing inference even when the bond’s own spread is unobserved. Empirically, the JD distortion model systematically outperforms both the canonical Wang transform and the raw expected loss in in-sample and out-of-sample tests, capturing discontinuous repricing and tail-risk compensation with greater precision. Extending the framework to a multifactor specification that combines actuarial fundamentals with financial-market covariates further enhances explanatory and predictive performance. From a methodological perspective, the RNN serves as a structural estimator for the parameters of the distortion operators, achieving higher accuracy, stability, and computational efficiency than conventional approaches such as MLE, GMM, or ensemble regressors. By unifying distortion operators with neural estimation, this study advances both the methodological and empirical foundations of CAT bond pricing within actuarial science.

A trace of a sequence is generated by deleting each bit of the sequence independently with a fixed probability. The well-studied trace reconstruction problem asks how many traces are required to reconstruct an unknown binary sequence with high probability. In this paper, we study the multidimensional version of this problem for matrices and hypermatrices, where a trace is generated by deleting each row/column of the matrix or each slice of the hypermatrix independently with a constant probability. Previously, Krishnamurthy, Mazumdar, McGregor and Pal showed that $\exp (\widetilde {O}(n^{d/(d+2)}))$ traces suffice to reconstruct any unknown $n\times n$ matrix (for $d=2$) and any unknown $n^{\times d}$ hypermatrix. By developing a dimension reduction procedure and establishing a multivariate version of the Littlewood-type result that lower bounds sparse complex polynomials around $1$, we improve this upper bound by showing that $\exp (\widetilde {O}(n^{3/7}))$ traces suffice to reconstruct any unknown $n\times n$ matrix, and $\exp (\widetilde {O}(n^{3/5}))$ traces suffice to reconstruct any unknown $n^{\times d}$ hypermatrix. In contrast to the earlier bound, our new exponent is bounded away from $1$ even as $d$ becomes very large.

Orthopaedic inpatients have distinct clinical traits. This study aimed to quantify the burden of nosocomial infections (NIs) on orthopaedic patients. A nested case–control study (2022–2024) at the China National Orthopaedic Medical Center compared orthopaedic inpatients with and without NIs and matched cases and controls 1:3 to evaluate the burden of NIs. A national economic burden analysis was subsequently conducted under various scenarios. Among 120,764 eligible patients, 338 (0.28%) developed NIs. A total of 321 cases were matched with 916 controls. The economic and temporal burdens of NIs are US$2,100 and 5 days per case respectively. Haematologic NIs had the highest additional cost (US$4,295) and the second longest extended stay (9 days). In terms of initial hospitalisations and readmissions, surgical site infections extended hospital stays by 20 days and increased costs by US$4,881. The top three diagnosis-related groups (DRGs) with high burdens are ZC11, ZJ15, and IE21 for costs and ZJ15, IE21, and IB19 for duration. In the mixed-region scenario, orthopaedic specialty hospitals nationwide incur US$5.23 million in direct medical costs annually because of NIs. These findings indicate that NIs significantly affect orthopaedic patients both individually and nationally, necessitating focused prevention and control for high-burden DRGs and specific infections.