Showing papers on "Matching (statistics) published in 2002"

Estimation of average treatment effects based on propensity scores

Abstract: In this paper, we give a short overview of some propensity score matching estimators suggested in the evaluation literature, and we provide a set of Stata programs, which we illustrate using the Na...

Alternative Approaches to Evaluation in Empirical Microeconomics

Abstract: Four alternative but related approaches to empirical evaluation of policy interventions are studied: social experiments, natural experiments, matching methods, and instrumental variables. In each case the necessary assumptions and the data requirements are considered for estimation of a number of key parameters of interest. These key parameters include the average treatment effect, the treatment on the treated and the local average treatment effect. Some issues of implementation and interpretation are discussed drawing on the labour market programme evaluation literature.

Multi-view Matching for Unordered Image Sets, or How Do I Organize My Holiday Snaps?

Abstract: There has been considerable success in automated reconstruction for image sequences where small baseline algorithms can be used to establish matches across a number of images. In contrast in the case of widely separated views, methods have generally been restricted to two or three views.In this paper we investigate the problem of establishing relative viewpoints given a large number of images where no ordering information is provided. A typical application would be where images are obtained from different sources or at different times: both the viewpoint (position, orientation, scale) and lighting conditions may vary significantly over the data set.Such a problem is not fundamentally amenable to exhaustive pair wise and triplet wide baseline matching because this would be prohibitively expensive as the number of views increases. Instead, we investiate how a combination of image invariants, covariants, and multiple view relations can be used in concord to enable efficient multiple view matching. The result is a matching algorithm which is linear in the number of views.The methods are illustrated on several real image data sets. The output enables an image based technique for navigating in a 3D scene, moving from one image to whichever image is the next most appropriate.

Feature selection algorithms: a survey and experimental evaluation

Abstract: In view of the substantial number of existing feature selection algorithms, the need arises to count on criteria that enables to adequately decide which algorithm to use in certain situations. This work assesses the performance of several fundamental algorithms found in the literature in a controlled scenario. A scoring measure ranks the algorithms by taking into account the amount of relevance, irrelevance and redundance on sample data sets. This measure computes the degree of matching between the output given by the algorithm and the known optimal solution. Sample size effects are also studied.

Larks: Dynamic Matchmaking Among Heterogeneous Software Agents in Cyberspace

Abstract: Service matchmaking among heterogeneous software agents in the Internet is usually done dynamically and must be efficient. There is an obvious trade-off between the quality and efficiency of matchmaking on the Internet. We define a language called Larks for agent advertisements and requests, and present a flexible and efficient matchmaking process that uses Larks. The Larks matchmaking process performs both syntactic and semantic matching, and in addition allows the specification of concepts (local ontologies) via ITL, a concept language. The matching process uses five different filters: context matching, profile comparison, similarity matching, signature matching and constraint matching. Different degrees of partial matching can result from utilizing different combinations of these filters. We briefly report on our implementation of Larks and the matchmaking process in Java. Fielded applications of matchmaking using Larks in several application domains for systems of information agents are ongoing efforts.

Defined Contribution Pensions: Plan Rules, Participant Decisions, and the Path of Least Resistance

Abstract: We assess the impact on savings behavior of several different 401(k) plan features, including automatic enrollment, automatic cash distributions, employer matching provisions, eligibility requirements, investment options, and financial education. We also present new survey evidence on individual savings adequacy. Many of our conclusions are based on an analysis of micro-level administrative data on the 401(k) savings behavior of employees in several large corporations that implemented changes in their 401(k) plan design.Our analysis identifies a key behavioral principle that should partially guide the design of 401(k) plans: employees often follow "the path of least resistance." For better or for worse, plan administrators can manipulate the path of least resistance to powerfully influence the savings and investment choices of their employees.

Simple and Bias-Corrected Matching Estimators for Average Treatment Effects

Abstract: Matching estimators for average treatment effects are widely used in evaluation research despite the fact that their large sample properties have not been established in many cases. In this article, we develop a new framework to analyze the properties of matching estimators and establish a number of new results. First, we show that matching estimators include a conditional bias term which may not vanish at a rate faster than root-N when more than one continuous variable is used for matching. As a result, matching estimators may not be root-N-consistent. Second, we show that even after removing the conditional bias, matching estimators with a fixed number of matches do not reach the semiparametric efficiency bound for average treatment effects, although the efficiency loss may be small. Third, we propose a bias-correction that removes the conditional bias asymptotically, making matching estimators root-N-consistent. Fourth, we provide a new estimator for the conditional variance that does not require consistent nonparametric estimation of unknown functions. We apply the bias-corrected matching estimators to the study of the effects of a labor market program previously analyzed by Lalonde (1986). We also carry out a small simulation study based on Lalonde's example where a simple implementation of the biascorrected matching estimator performs well compared to both simple matching estimators and to regression estimators in terms of bias and root-mean-squared-error. Software for implementing the proposed estimators in STATA and Matlab is available from the authors on the web.

Comparison of Schema Matching Evaluations

Abstract: Recently, schema matching has found considerable interest in both research and practice. Determining matching components of database or XML schemas is needed in many applications, e.g. for E-business and data integration. Various schema matching systems have been developed to solve the problem semi-automatically. While there have been some evaluations, the overall effectiveness of currently available automatic schema matching systems is largely unclear. This is because the evaluations were conducted in diverse ways making it difficult to assess the effectiveness of each single system, let alone to compare their effectiveness. In this paper we survey recently published schema matching evaluations. For this purpose, we introduce the major criteria that influence the effectiveness of a schema matching approach and use these criteria to compare the various systems. Based on our observations, we discuss the requirements for future match implementations and evaluations.

Endogenous matching and the empirical determinants of contract form

Abstract: Empirical work on contracts typically regresses contract choice on observed principal and agent characteristics. If (i) some of these characteristics are unobserved or partially observed and (ii) there are incentives whereby particular types of agents end up contracting with particular types of principals, estimated coefficients on the observed characteristics may be misleading. We address this endogenous matching problem using a data set on agricultural contracts between landlords and tenants in early Renaissance Tuscany. Controlling for endogenous matching has an impact on parameters of interest, and tenants’ risk aversion appears to have influenced contract choice.

Some practical issues in the evaluation of heterogeneous labour market programmes by matching methods

Abstract: Not available in German. Recently several studies analysed active labour market policies using a newly proposed matching estimator for multiple programmes. Since there is only very limited practical experience with this estimator, this paper checks its sensitivity with respect to issues that are of practical importance. The estimator turns out to be fairly robust to several matters that concern its implementation. Furthermore, the paper demonstrates that the matching approach per se is no magic bullet solving all problems of evaluation studies, but that its success depends critically on the information available in the sample. Finally, a comparison with a bootstrap distribution provides some justification for using a simplified approximation of the distribution of the estimator that ignores its sequential nature.

A matching model with endogenous skill requirements

Abstract: We consider a labor market in which workers differ in their abilities and jobs differ in their skill requirements. The distribution of worker abilities is exogenous, but we model the choice of skill requirements by firms. High-skill jobs produce more output than low-skill jobs, but high-skill jobs require high-skill workers and thus are more difficult to fill. We use a matching model together with a Nash bargaining approach to wage setting to determine the equilibrium mix of job types, along with the equilibrium relationship between worker and job characteristics, wages, and unemployment.

Methods for matching, selecting, narrowcasting, and/or classifying based on rights management and/or other information

Abstract: Rights management information is used at least in part in a matching, narrowcasting, classifying and/or selecting process. A matching and classification utility system comprising a kind of Commerce Utility System is used to perform the matching, narrowcasting, classifying and/or selecting. The matching and classification utility system may match, narrowcast, classify and/or select people and/or things, non-limiting examples of which include software objects. The Matching and Classification Utility system may use any pre-existing classification schemes, including at least some rights management information and/or other qualitative and/or parameter data indicating and/or defining classes, classification systems, class hierarchies, category schemes, class assignments, category assignments, and/or class membership. The Matching and Classification Utility may also use at least some rights management information together with any artificial intelligence, expert system, statistical, computational, manual, or any other means to define new classes, class hierarchies, classification systems, category schemes, and/or assign persons, things, and/or groups of persons and/or things to at least one class.

Simple and Bias-Corrected Matching Estimators for Average Treatment Effects

Abstract: Matching estimators for average treatment effects are widely used in evaluation research despite the fact that their large sample properties have not been established in many cases. In this article, we develop a new framework to analyze the properties of matching estimators and establish a number of new results. First, we show that matching estimators include a conditional bias term which may not vanish at a rate faster than root-N when more than one continuous variable is used for matching. As a result, matching estimators may not be root-N-consistent. Second, we show that even after removing the conditional bias, matching estimators with a fixed number of matches do not reach the semiparametric efficiency bound for average treatment effects, although the efficiency loss may be small. Third, we propose a bias-correction that removes the conditional bias asymptotically, making matching estimators root-N-consistent. Fourth, we provide a new estimator for the conditional variance that does not require consistent nonparametric estimation of unknown functions. We apply the bias-corrected matching estimators to the study of the effects of a labor market program previously analyzed by Lalonde (1986). We also carry out a small simulation study based on Lalonde's example where a simple implementation of the biascorrected matching estimator performs well compared to both simple matching estimators and to regression estimators in terms of bias and root-mean-squared-error. Software for implementing the proposed estimators in STATA and Matlab is available from the authors on the web.

Assessing Viability and Sustainability: a Systems-based Approach for Deriving Comprehensive Indicator Sets

Abstract: Introduction Method Reality as a nested system of nested systems Matching a system to its environment: viability and basic orientors Using basic orientors to guide indicator selection Measuring Viability and Performance Results Indicators of sustainable development for a region Formalized quantitative performance assessment Discussion Responses to this Article Acknowledgments Literature Cited

Competitive pricing and efficiency in search equilibrium

Abstract: We consolidate and generalize some results on price determination and efficiency in search equilibrium. Extending models by Rubinstein and Wolinsky and by Gale, heterogeneous buyers and sellers meet according to a general matching technology and prices are determined by a general bargaining condition. When the discount rate r and search costs converge to 0, we show that prices in all exchanges are the same and equal the competitive, market clearing, price. Given positive search costs, efficiency obtains iff bargaining satisfies Hosios' condition and r=0. When prices are set by third-party market makers, however, we show that search equilibrium is necessarily efficient.

Surface signatures: an orientation independent free-form surface representation scheme for the purpose of objects registration and matching

Abstract: This paper introduces anew free-form surface representation scheme for the purpose of fast and accurate registration and matching. Accurate registration of surfaces is a common task in computer vision. The proposed representation scheme captures the surface curvature information (seen from certain points) and produces images, called "surface signatures," at these points. Matching signatures of different surfaces enables the recovery of the transformation parameters between these surfaces. We propose using template matching to compare the signature images. To enable partial matching, another criterion, the overlap ratio is used. This representation scheme can be used as a global representation of the surface as well as a local one and performs near real-time registration. We show that the signature representation can be used to recover scaling transformation as well as matching objects in 3D scenes in the presence of clutter and occlusion. Applications presented include: free-form object matching, multimodal medical volumes registration, and dental teeth reconstruction from intraoral images.

Application of dynamic programming to the correlation of paleoclimate records

Abstract: [1] Signal matching is a powerful tool frequently used in paleoclimate research, but it is enormously time-consuming when performed by hand. Previously proposed automatic correlation techniques require very good initial fits to find the correct alignment of two records. A new technique presented in this paper utilizes dynamic programming to find the globally optimal alignment of two records. Geological realism is instilled in the solution through the definition of penalty functions for undesirable behavior such as unlikely changes in accumulation rate. Examples with synthetic and real data demonstrate that the dynamic programming technique produces accurate, high-resolution results with much less effort than hand tuning or preexisting automated correlation techniques.

Defined Contribution Pensions: Plan Rules, Participant Choices, and the Path of Least Resistance

Abstract: We assess the effect on savings behavior of several different 401(k) plan features, including automatic enrollment, automatic cash distributions, employer matching provisions, eligibility requirements, investment options, and financial education. We also present new survey evidence on individual savings adequacy. Many of our conclusions are based on an analysis of micro-level administrative data on the 401(k) savings behavior of employees in several large corporations that implemented changes in their 401(k) plan design. Our analysis identifies a key behavioral principle that should partially guide the design of 401(k) plans: employees often follow the path of least resistance. For better or for worse, plan administrators can manipulate the path of least resistance to powerfully influence the savings and investment choices of their employees.

Awarded Best Student Paper! - Track-Aligned Extents: Matching Access Patterns to Disk Drive Characteristics

Abstract: Track-aligned extents (traxtents) utilize disk-specific knowledge to match access patterns to the strengths of modern disks. By allocating and accessing related data on disk track boundaries, a system can avoid most rotational latency and track crossing overheads. Avoiding these overheads can increase disk access efficiency by up to 50% for mid-sized requests (100–500 KB). This paper describes traxtents, algorithms for detecting track boundaries, and some uses of traxtents in file systems and video servers. For large-file workloads, a version of FreeBSD’s FFS implementation that exploits traxtents reduces application run times by up to 20% compared to the original version. A video server using traxtent-based requests can support 56% more concurrent streams at the same startup latency and buffer space. For LFS, 44% lower overall write cost for track-sized segments can be achieved.

Overt Bias in Observational Studies

Abstract: An observational study is biased if the treated and control groups differ prior to treatment in ways that matter for the outcomes under study. An overt bias is one that can be seen in the data at hand-for instance, prior to treatment, treated subjects are observed to have lower incomes than controls. A hidden bias is similar but cannot be seen because the required information was not observed or recorded. Overt biases are controlled using adjustments, such as matching or stratification. In other words, treated and control subjects may be seen to differ in terms of certain observed covariates, but these visible differences may be removed by comparing treated and control subjects with the same values of the observed covariates, that is, subjects in the same matched set or stratum defined by the observed covariates. It is natural to ask when the standard methods for randomized experiments may be applied to matched or stratified data from an observational study. This chapter discusses a model for an observational study in which there is overt bias but no hidden bias. The model is, at best, one of many plausible models, but it does clarify when methods for randomized experiments may be used in observational studies, and so it becomes the starting point for thinking about hidden biases. Dealing with hidden bias is the focus of most of the later chapters.

Weighted range sensor matching algorithms for mobile robot displacement estimation

Abstract: Introduces a "weighted" matching algorithm to estimate a robot's planar displacement by matching two-dimensional range scans. The influence of each scan point on the overall matching error is weighted according to its uncertainty. We develop uncertainty models that account for effects such as measurement noise, sensor incidence angle, and correspondence error. Based on models of expected sensor uncertainty, our algorithm computes the appropriate weighting for each measurement so as to optimally estimate the displacement between two consecutive poses. By explicitly modeling the various noise sources, we can also calculate the actual covariance of the displacement estimates instead of a statistical approximation of it. A realistic covariance estimate is necessary for further combining the pose displacement estimates with additional odometric and/or inertial measurements within a localization framework. Experiments using a Nomad 200 mobile robot and a Sick LMS-200 laser range finder illustrate that the method is more accurate than prior techniques.

Fingerprint matching using ridge feature maps

Abstract: A method for matching fingerprint images is provided. The method includes the steps of acquiring a query image of a fingerprint; extracting a minutiae set from the query image; comparing the minutiae set of the query image with a minutiae set of at least one template image to determine transformation parameters to align the query image to the at least one template image and to determine a minutiae matching score; constructing a ridge feature map of the query image; comparing the ridge feature map of the query image to a ridge feature map of the at least one template image to determine a ridge feature matching score; and combining the minutiae matching score with the ridge feature matching score resulting in an overall score, the overall score being compared to a threshold to determine if the query image and the at least one template image match.

Extensive Games as Process Models

Abstract: We analyze extensive games as interactive process models, using modal languages plus matching notions of bisimulation as varieties of game equivalences. Our technical results show how to fit existing modal notions into this new setting.

An application of the matching law to severe problem behavior

Abstract: We evaluated problem behavior and appropriate behavior using the matching equation with 4 individuals with developmental disabilities. Descriptive observations were conducted during interactions between the participants and their primary care providers in either a clinical laboratory environment (3 participants) or the participant's home (1 participant). Data were recorded on potential reinforcers, problem behavior, and appropriate behavior. After identifying the reinforcers that maintained each participant's problem behavior by way of functional analysis, the descriptive data were analyzed retrospectively, based on the matching equation. Results showed that the proportional rate of problem behavior relative to appropriate behavior approximately matched the proportional rate of reinforcement for problem behavior for all participants. The results extend prior research because a functional analysis was conducted and because multiple sources of reinforcement (other than attention) were evaluated. Methodological constraints were identified, which may limit the application of the matching law on both practical and conceptual levels.

A matching advantage for dynamic human faces.

Abstract: In a series of three experiments, we used a sequential matching task to explore the impact of non-rigid facial motion on the perception of human faces. Dynamic prime images, in the form of short video sequences, facilitated matching responses relative to a single static prime image. This advantage was observed whenever the prime and target showed the same face but an identity match was required across expression (experiment 1) or view (experiment 2). No facilitation was observed for identical dynamic prime sequences when the matching dimension was shifted from identity to expression (experiment 3). We suggest that the observed dynamic advantage, the first reported for non-degraded facial images, arises because the matching task places more emphasis on visual working memory than typical face recognition tasks. More specifically, we believe that representational mechanisms optimised for the processing of motion and/or change-over-time are established and maintained in working memory and that such ‘dynamic r...

Finding the Largest Unambiguous Component of Stereo Matching

Abstract: Stereo matching is an ill-posed problem for at least two principal reasons: (1) because of the random nature of match similarity measure and (2) because of structural ambiguity due to repetitive patterns. Both ambiguities require the problem to be posed in the regularization framework. Continuity is a natural choice for a prior model. But this model may fail in low signal-to-noise ratio regions. The resulting artefacts may then completely spoil the subsequent visual task.A question arises whether one could (1) find the unambiguous component of matching and, simultaneously, (2) identify the ambiguous component of the solution and then, optionally, (3) regularize the taskfor the ambiguous component only. Some authors have already taken this view. In this paper we define a new stability property which is a condition a set of matches must satisfy to be considered unambiguous at a given confidence level. It turns out that for a given matching problem this set is (1) unique and (2) it is already a matching. We give a fast algorithm that is able to find the largest stable matching. The algorithm is then used to show on real scenes that the unambiguous component is quite dense (10-80%) and error-free (total error rate of 0.3-1.4%), both depending on the confidence level chosen.

Monotone Matching in Perfect and Imperfect Worlds

Abstract: We study frictionless matching in large economies with and without market imperfections, providing sufficient conditions for monotone matching that are weaker than those previously known. Necessary conditions, which depend on a key analytical object we call the surplus function, are also offered. Changes in the surplus yield valuable information about the comparative statics of matching patterns across environments. We apply our framework to some examples adapted from the literature, accounting for and extending several comparative-static and welfare results. We also explore the dependence of the matching pattern on the type distribution.