SFA Models Research Articles

Superficial femoral artery stenting: Impact of stent design and overlapping on the local hemodynamics

BackgroundSuperficial femoral arteries (SFAs) treated with self-expanding stents are widely affected by in-stent restenosis (ISR), especially in case of long lesions and multiple overlapping devices. The altered hemodynamics provoked by the stent is considered as a promoting factor of ISR. In this context, this work aims to analyze the impact of stent design and stent overlapping on patient-specific SFA hemodynamics. MethodsThrough a morphing technique, single or multiple stents were virtually implanted within two patient-specific, post-operative SFA models reconstructed from computed tomography. The stented domains were used to perform computational fluid dynamics simulations, quantifying wall shear stress (WSS) based descriptors including time-averaged WSS (TAWSS), oscillatory shear index (OSI), transverse WSS (transWSS), and WSS ratio (WSSRATIO). Four stent designs (three laser-cut – EverFlex, Zilver and S.M.A.R.T. – and one prototype braided stent), and three typical clinical scenarios accounting for different order of stent implantation and overlapping length were compared. ResultsThe main hemodynamic differences were found between the two types of stent designs (i.e. laser-cut vs. braided stents). The braided stent presented lower median transWSS and higher median WSSRATIO than the laser-cut stents (p < 0.0001). The laser-cut stents presented comparable WSS-based descriptor values, except for the Zilver, exhibiting a median TAWSS ∼30% higher than the other stents. Stent overlapping provoked an abrupt alteration of the WSS-based descriptors. The overlapping length, rather than the order of stent implantation, highly and negatively impacted the hemodynamics. ConclusionThe proposed computational workflow compared different SFA stent designs and stent overlapping configurations, highlighting those providing the most favorable hemodynamic conditions.

Сучасні підходи до оцінювання енергоефективності національної економіки

The article notes that energy efficiency cannot simply be a vague and ambiguous concept that does not have accurate assessment methods. It should have clear measurements and evaluation methods. When the question arises as to measuring or evaluating, the lack of a clear definition of energy efficiency can cause the results to differ and it will be difficult to compare them depending on the needs or objectives. So the need to develop an accurate and unified definition of energy efficiency, as well as its classification and development of measurement methods is highlighted. It is emphasized that highly developed countries of the world have significant experience in achieving a high level of energy efficiency of national economies, but they also do not currently have developed a unified system of energy efficiency indicators at the national level, methods for their assessment and analysis. The energy intensity of GDP is almost the only universal instrument by which international and regional comparisons of energy efficiency levels of national economies are possible. It is shown that in recent years in Ukraine there has been a clear tendency to reduce the energy intensity of the national economy in almost all spheres. The State Agency on Energy Efficiency and Energy Saving of Ukraine has developed tables of primary data and a methodology for calculating energy efficiency indicators of the Ukrainian economy. Primary data and calculation indicators are formed by such sectors as industry, transport, housing, agriculture, services. The article shows that recent methods for evaluating energy efficiency based on modeling the efficiency limit, namely, DEA and SFA models, have become a popular tool for evaluating energy efficiency. Despite a number of its advantages, the DEA method does not take into account statistical noise. In contrast to DEA models, SFA models use the Shepard distance function to determine the energy efficiency index and take into account statistical noise.

Technical efficiency and inefficiency: Reliability of standard SFA models and a misspecification problem

It is formally proven that if inefficiency (u) is modelled through its variance, considered as a function of exogenous variables z, then the marginal effects of z on technical inefficiency (TI) and technical efficiency (TE) have opposite signs in the typical setup with a normally distributed random error and an exponentially or half-normally distributed u. This is true for both conditional and unconditional TI and TE. An example is provided to show that the signs of the marginal effects of z on TI and TE may coincide for some ranges of z. If the real data comes from a bimodal distribution of u, and a model is estimated with an exponential or half-normal distribution for u, the estimated efficiency and the marginal effect of z on TE could be wrong. Moreover, the rank correlations between the true and the estimated values of TE could be small and even negative for some subsamples of the data. This is a warning that in the case when the true (real life) distribution of the inefficiency is bimodal, commonly used standard SFA models could lead to wrong policy recommendations. The kernel density plot of the residuals is suggested as a diagnostic plot. The results are illustrated by simulations.

Dynamic network DEA and SFA models for accounting and financial indicators with an analysis of super-efficiency in stochastic frontiers: An efficiency comparison in OECD banking

This paper presents an assessment of 124 OECD banks during 2004–2013 in light of relevant accounting and financial indicators that reflect banking production process and performance. Novel DEA and SFA Dynamic Network Super-efficiency models are developed to handle the underlying relationships among major accounting and financial indicators. Additionally, we develop a novel super-efficiency concept for SFA to compare DEA and SFA on common grounds to the extent possible. Firstly, a relational model encompassing major profit sheet indicators, balance sheet indicators, and net income is presented under a dynamic network structure for both models under the non-parametric and parametric specifications. Subsequently, the dynamic effect of carry-over indicators is incorporated into them, so that efficiency scores can be properly computed for these three sub-structures. Differences in scores and ranks are explored by bootstrapped regressions. It reveals that results generated from the proposed models interact differently with the socio-economic and business-related variables.

Evaluating Technical Efficiency of Stock Performance using Copula-Based Stochastic Frontier Analysis Approach

This study estimates the technical efficiency for 14 selected Malaysian trading and services companies for 2017 and 2018 using the Cobb-Douglas with the Stochastic Frontier production model. In standard stochastic frontier analysis (SSFA), the two-sided error, statistical noise, and one-sided error, inefficiency term are assumed to be independent. The assumption for statistical noise is normally distributed and the inefficiency term is half-normal distributed. In this paper, the copula model is applied to capture the joint distribution of these two error components. The copula model is an alternative method that is able to account for the joint multivariate distribution. Copula functions can be used to capture rank correlation and tail dependence between two error components, thus making the SFA more flexible. Seven copula models from the Archimedean copula family are considered in this study including the copulas with the trigonometric and hyperbolic generator. This study further compares the technical efficiency yielded by copulas with standard SFA, DEA-CCR and DEA-BCC models. The results raise the question of the reliability of SFA based on the standard model. Since the dependence error between statistical noise and inefficiency error cannot be ignored, the copula-based in SFA models can be considered as an alternative suitable tool for measuring efficiency performance.

Multimodal Miniature Surface Forces Apparatus (μSFA) for Interfacial Science Measurements.

Advances in the research of intermolecular and surface interactions result from the development of new and improved measurement techniques and combinations of existing techniques. Here, we present a new miniature version of the surface forces apparatus-the μSFA-that has been designed for ease of use and multimodal capabilities with the retention of the capabilities of other SFA models including accurate measurements of the surface separation distance and physical characterization of dynamic and static physical forces (i.e., normal, shear, and friction) and interactions (e.g., van der Waals, electrostatic, hydrophobic, steric, and biospecific). The small physical size of the μSFA, compared to previous SFA models, makes it portable and suitable for integration into commercially available optical and fluorescence light microscopes, as demonstrated here. The large optical path entry and exit ports make it ideal for concurrent force measurements and spectroscopy studies. Examples of the use of the μSFA in combination with surface plasmon resonance (SPR) and Raman spectroscopy measurements are presented. Because of the short working distance constraints associated with Raman spectroscopy, an interferometric technique was developed and applied to calculate the intersurface separation distance based on Newton's rings. The introduction of the μSFA will mark a transition in SFA usage from primarily physical characterization to concurrent physical characterization with in situ chemical and biological characterization to study interfacial phenomena, including (but not limited to) molecular adsorption, fluid flow dynamics, the determination of surface species and morphology, and (bio)molecular binding kinetics.

Evaluation of profit efficiency of Ukrainian banks on the base of SFA models

The article analyzes the profit efficiency of the Ukrainian banks by means of a constructed model of stochastic efficiency frontier on the basis of intermediary approach. For constructing of the trans-logarithmic function for the efficiency frontier, the concept of alternative profit efficiency was applied. We used the value of fixed assets, labor costs, the cost of loan capital as input variables, whereas output variables were: issued loans, other assets and total costs. The analysis of the profit efficiency of the Ukrainian banks in 2015 and 2016 pointed out to a number of serious problems in the domestic banking sector. Primarily, the system’s average efficiency in general was quite low and constituted only 0.31. Of particular concern is actually the zero efficiency of the Ukrainian state-owned banks. In contrast to the latter and subsidiaries of foreign banking groups the Ukrainian banks with private capital have showed a slightly higher level of profitability over the analyzed period.

Sales Force Automation dalam Peningkatan Pelayanan Terhadap Pelanggan

The purpose of this research is to analyze the company's business processes in managing customers, and design e-crm system in the field of Sales Force Automation. The method used in this research is to study literature to see SFA models to be applied, the collection of data by conducting surveys, interviews with the company as well as designing the SFA system that includes the necessary features, system design, class diagrams, sequence diagrams and screen design. The analysis of the system running can be identified problems in PT. LKI is lack of features that facilitate the company's internal applications as well as with clients in the execution of projects and no lesson learned or report that contains the project sales and employee performance. Based on the results of the research it can be concluded that PT. LKI Is required the application of Sales Force Automation that helps clients get information about the project that is being worked on, facilitates communication between internal and with clients and have a report of corporate performance as well as employees in order to achieve and enhance the company strategy in order to provide the best service for clients.&#x0D; Index Terms— e-CRM, Sales Force Automation

Measuring Patient Satisfaction's Relationship to Hospital Cost Efficiency: Can Administrators Make a Difference?

The aim of this study was to assess the ability and means by which hospital administrators can influence patient satisfaction and its impact on costs. Data are drawn from the American Hospital Association's Annual Survey of Hospitals, federally collected Hospital Cost Reports, and Medicare's Hospital Compare. Stochastic frontier analyses (SFA) are used to test the hypothesis that the patient satisfaction-hospital cost relationship is primarily a latent "management effect." The null hypothesis is that patient satisfaction measures are main effects under the control of care providers rather than administrators. Both SFA models were superior to the standard regression analysis when measuring patient satisfaction's relationship to hospitals' cost efficiency. The SFA model with patient satisfaction measures treated as main effects, rather than "latent, management effects," was significantly better comparing the log-likelihood statistics. Higher patient satisfaction scores on the environmental quality and provider communication dimensions were related to lower facility costs. Higher facility costs were positively associated with patients' overall impressions (willingness to recommend and overall satisfaction), assessments of medication and discharge instructions, and ratings of caregiver responsiveness (pain control and help when called). In the short term, managers have a limited ability to influence patient satisfaction scores, and it appears that working through frontline providers (doctors and nurses) is critical to success. In addition, results indicate that not all patient satisfaction gains are cost neutral and there may be added costs to some forms of quality. Therefore, quality is not costless as is often argued.

FISCAL SPACE FOR HEALTH IN SUB-SAHARAN AFRICAN COUNTRIES: AN EFFICIENCY APPROACH

The study argues that potential savings from efficiency could be effective alternative to increasing health system financing in SSA. Health system efficiency estimates were derived from the Data Envelopment Analysis and Stochastic Frontier Analysis and used to compute potential gains from efficiency. Data was sourced from the World Bank's world development indicators for 45 SSA countries in 2011. The results reveal that average potential saving in health expenditure from improved efficiency was 0.10% and 0.75% of GDP per capita in the DEA and SFA models, respectively. The results also showed that a 1% increase in efficiency of health expenditure reduced infant mortality rate by 0.91% compared to 0.40% reduction in infant mortality if health expenditure increased by 1%. The results imply that in the face of significant economic challenges and burden on government budget, improving health expenditure efficiency to create some fiscal space will be an important step.

Efficiency and Integration in the Food Supply Chain

Due to the nature of the food supply chain, an increase of the integration's degree in the chain may be an important aspect in the context of increasing the efficiency of agri-food companies. Therefore, exploring the relationships among these variables was found as an important research area and adopted as the goal of the paper. The paper is focused mainly on the theoretical background showing the relationship between integration and performance. A description of the theoretical and methodological aspects of performance measurement and its extension (including the integration aspect) was also made within the framework of the paper. For an empirical illustration of the analyzed relationships two steps were made. Firstly, the integration's degree in the food chain was measured. Secondly, the efficiency of the companies from the cereals processing industry in Europe was assessed. The SFA models (e.g. Translog and Cobb-Douglas functional form) were used for assessment of efficiency. By using stochastic method (e.g. the SFA, Stochastic Frontier Analysis), one may show the influence of external variable (the integration in the supply chain) on the efficiency performance of enterprises. Efficiency of economic entities is not an unambiguous term. There are several different concepts of efficiency, its measurement and expressions. Within the framework of efficiency, many terms of similar meaning may be applied. However, these concepts are not identical. The actual concept of efficiency is derived from the structure of the production function, therefore it is conditioned by changes in the productivity of production factors and their remuneration and refers to the allocation of production factors in the most technically efficient way.

Understanding prediction intervals for firm specific inefficiency scores from parametric stochastic frontier models

This paper makes two important contributions to the literature on prediction intervals for firm specific inefficiency estimates in cross sectional SFA models. Firstly, the existing intervals in the literature do not correspond to the minimum width intervals and in this paper we discuss how to compute such intervals and how they either include or exclude zero as a lower bound depending on where the probability mass of the distribution of \( u_{i} |\varepsilon_{i} \) resides. This has useful implications for practitioners and policy makers, with greatest reductions in interval width for the most efficient firms. Secondly, we propose an ‘asymptotic’ approach to incorporating parameter uncertainty into prediction intervals for firm specific inefficiency (given that in practice model parameters have to be estimated) as an alternative to the ‘bagging’ procedure suggested in Simar and Wilson (Econom Rev 29(1):62–98, 2010). The approach is computationally much simpler than the bagging approach.

One-step and two-step estimation in SFA models

One-step and two-step estimation in SFA models

Impact of Implementation of Case-mix System on Efficiency of a Teaching Hospital in Malaysia

University Kebangsaan Malaysia Medical Center (UKMMC) is the first government hospital in Malaysia which has taken the initiative to implement the case-mix system since July 2002. Established in 1997, this 873 bed teaching hospital provides tertiary level services to around 600,000 people in two southern districts of Federal Territory Kuala Lumpur. The objective of this research is to assess the impact of implementation of case-mix system on efficiency of clinical services provided by UKMMC using Stochastic Frontier Analysis. The hypothesis for this study is that the implementation of case-mix system has improved the level of efficiency at UKMMC. Results of SFA models proved that implementation of case-mix system have decreased the technical inefficiency 1.93 percent yearly during study period at UKMMC.

Bayesian and DEA efficiency modelling: an application to hospital foodservice operations

The significant impact of health foodservice operations on the total operational cost of the hospital sector has increased the need to improve the efficiency of these operations. Although important studies on the performance of foodservice operations have been published in various academic journals and industrial reports, the findings and implications remain simple and limited in scope and methodology. This paper investigates two popular methodologies in the efficiency literature: Bayesian “stochastic frontier analysis” (SFA) and “data envelopment analysis” (DEA). The paper discusses the statistical advantages of the Bayesian SFA and compares it with an extended DEA model. The results from a sample of 101 hospital foodservice operations show the existence of inefficiency in the sample, and indicate significant differences between the average efficiency generated by the Bayesian SFA and DEA models. The ranking of efficiency is, however, statistically independent of the methodologies.

The Cost Efficiency of the Brazilian Electricity Distribution Utilities: A Comparison of Bayesian SFA and DEA Models

The purpose of this study is to evaluate the efficiency indices for 60 Brazilian electricity distribution utilities. These scores are obtained by DEA (Data Envelopment Analysis) and Bayesian Stochastic Frontier Analysis models, two techniques that can reduce the information asymmetry and improve the regulator′s skill to compare the performance of the utilities, a fundamental aspect in incentive regulation schemes. In addition, this paper also addresses the problem of identifying outliers and influential observations in deterministic nonparametric DEA models.

Comparative analysis of phosphorus use within national and local economies in China

Material/substance flow analysis (MFA/SFA) approaches have been broadly applied to bridge the knowledge gaps in material metabolism within modern economies—and the environmental consequences it cause. While the structural feature of material use can vary along a physical dimension, there is a need to analytically normalize the implications derived from various material flow models to facilitate policy making, with respect to the associated socio-economic profiles. This is particularly important in accounting for material throughput, given various data uncertainties. This study attempts to develop an illustrative framework combining the mass balance approach [Adriaanse A, Bringezu S, Hammond A, et al. Resource flows: the material basis of industrial economies. Washington, DC: World Resources Institute; 1997] and proposed material use indictors at a substance level. The methodology is then applied for the case of the phosphorus cycle in China, the largest developing country currently in transition. Our discussion is conducted on the basis of two updated static SFA models which have been developed recently [Liu Y, Mol APJ, Chen JN. Material flow and ecological restructuring in China: the case of phosphorus. J Ind Ecol 2004;8(3):103–20; Liu Y, Chen JN, Mol APJ. Evaluation of phosphorus flows in the Dianchi Watershed, southwest of China. Popul Environ 2004;25(6):637–56]. Taking mineral reserve, commodities trading and environmental accumulation into account, the aggregated physical features of phosphorus flows are identified at both the national and local levels, respectively, by treating the overall lifespan of substance use within these economies as a whole. Material use efficiencies of six subsystems – involving the phosphate industry, crop farming, intensive livestock husbandry, family-based animal rearing and urban and rural households – are analyzed. The results highlight that both the aggregate and sectoral features of phosphorus use varies significantly with the shift in geographic boundary from national to local economies. With respect to the substantial differentiations, the discussion on desired structural adjustment strategies and efficiency-enhancement options towards a systematical improvement of phosphorus use could facilitate future rational policy-making.

International benchmarking and regulation: an application to European electricity distribution utilities

Due to a shortage of data and increased international mergers, national energy regulators are looking to international benchmarking analyses for help in setting price controls within incentive regulation. We present an international benchmarking study of 63 regional electricity distribution utilities in six European countries that aims to illustrate the methodological and data issues encountered in the use of international benchmarking for utility regulation. The study examines the effect of the choice of benchmarking methods using DEA, COLS and SFA models. We discuss what problems of international benchmarking are highlighted by the study and how they can be overcome.

Material flows and economic models: an analytical comparison of SFA, LCA and partial equilibrium models

The growing concern for environmental problems in the current economy has spurred the study of the way materials and substances flow through the economy, resulting in many different types of analysis. Since all of these have their merits and shortcomings, much of the present theoretical research seems to be focusing on combining the best aspects of each model type into an integrated model. The aim of this paper is to make a first step in bridging the gap between the various types of analysis of material flows in the economy, by discussing the main differences and similarities of three often employed model types: substance flow analysis, life cycle assessment and partial economic equilibrium analysis. Instead of submitting each model to a lengthy theoretical discussion, we apply them to a single, hypothetical example of a pollution problem. By doing so we are able to evaluate the differences and similarities of the methods and results of the model in a practical way. It appears that the results of the three models are complementary rather than contradictory. Each of them puts an emphasis on different aspects of ‘the real world’. A sequential application of a number of limited models may therefore be an approach that provides more useful information than the tedious construction and application of an encompassing model that integrates these models.

Evaluations of candidate DGRF 1945, 1950, 1955 and 1960 models

The candidate models for the definitive geomagnetic reference field (DGRF) for the years 1945, 1950, 1955 and 1960—S45, 50, 55, 60, SFA45, 50, 55, 60, SFAS45, 50, 55, 60, and BGSMF50, 60—are evaluated using magnetic observatory data and observatory anomaly solutions given by the CSFC(9/80) and GSFC(12/83) models. The results indicate that the series of SFA models is the most successful series of models, and the BGSMF60 model is the best individual model, but the BGSMF50 model is less successful.