Showing papers on "Matching (statistics) published in 2000"

Secure data interchange

Abstract: A secure data interchange system enables information about bilateral and multilateral interactions between multiple persistent parties to be exchanged and leveraged within an environment that uses a combination of techniques to control access to information, release of information, and matching of information back to parties. Access to data records can be controlled using an associated price rule. A data owner can specify a price for different types and amounts of information access.

Hierarchies and the Organization of Knowledge in Production

Abstract: This paper studies how communication allows for the specialized acquisition of knowledge. It shows that a knowledge‐based hierarchy is a natural way to organize the acquisition of knowledge when matching problems with those who know how to solve them is costly. In such an organization, production workers acquire knowledge about the most common or easiest problems confronted, and specialized problem solvers deal with the more exceptional or harder problems. The paper shows that the model is consistent with stylized facts in the theory of organizations and uses it to analyze the impact of changes in production and information technology on organizational design.

Combining Propensity Score Matching with Additional Adjustments for Prognostic Covariates

Abstract: Propensity score matching refers to a class of multivariate methods used in comparative studies to construct treated and matched control samples that have similar distributions on many covariates. This matching is the observational study analog of randomization in ideal experiments, but is far less complete as it can only balance the distribution of observed covariates, whereas randomization balances the distribution of all covariates, both observed and unobserved. An important feature of propensity score matching is that it can be easily combined with model-based regression adjustments or with matching on a subset of special prognostic covariates or combinations of prognostic covariates that have been identified as being especially predictive of the outcome variables. We extend earlier results by developing approximations for the distributions of covariates in matched samples created with linear propensity score methods for the practically important situation where matching uses both the estimat...

Assortative Matching and Search

Abstract: In Becker's (1973) neoclassical marriage market model, matching is positively assortative if types are complements: i.e., match output f(x, y) is suipermoddlar in x and y. We reprise this famous result assuming time-intensive partner search and transferable output. We prove existence of a search equilibrium with a continuum of types, and then characterize matching. After showing that Becker's conditions on match output no longer suffice for assortative matching, we find sufficient conditions valid for any search frictions and type distribution: supermodularity not only of output f, but also of log f, and log f Symmetric submodularity conditions imply negatively assortative matching. Examples show these conditions are necessary.

Does Matching Overcome Lalonde's Critique of Nonexperimental Estimators?

Abstract: This paper applies recently developed cross-sectional and longitudinal propensity score matching estimators to data from the National Supported Work Demonstration that have been previously analyzed by LaLonde (1986) and Dehejia and Wahba (1998,1999). We find little support for recent claims in the econometrics and statistics literatures that traditional, cross-sectional matching estimators generally provide a reliable method of evaluating social experiments (e.g. Dehejia and Wahba, 1998, 1999). Our results show that program impact estimates generated through propensity score matching are highly sensitive to choice of variables used in estimating the propensity scores and sensitive to the choice of analysis sample. Among the estimators we study, the difference-in-differences matching estimator is the most robust. We attribute its better performance to the fact that it eliminates temporarily - invariant sources of bias that may arise, for example, when program participants and nonparticipants are geographically mismatched or from differences in survey questionnaires, which are both common sources of biases in evaluation studies.

A fingerprint verification system based on triangular matching and dynamic time warping

Abstract: An effective fingerprint verification system is presented. It assumes that an existing reference fingerprint image must validate the identity of a person by means of a test fingerprint image acquired online and in real-time using minutiae matching. The matching system consists of two main blocks: The first allows for the extraction of essential information from the reference image off-line, the second performs the matching itself online. The information is obtained from the reference image by filtering and careful minutiae extraction procedures. The fingerprint identification is based on triangular matching to cope with the strong deformation of fingerprint images due to static friction or finger rolling. The matching is finally validated by dynamic time warping. Results reported on the NIST Special Database 4 reference set, featuring 85 percent correct verification (15 percent false negative) and 0.05 percent false positive, demonstrate the effectiveness of the verification technique.

Estimating and Using Propensity Scores with Partially Missing Data

Abstract: Investigators in observational studies have no control over treatment assignment. As a result, large differences can exist between the treatment and control groups on observed covariates, which can lead to badly biased estimates of treatment effects. Propensity score methods are an increasingly popular method for balancing the distribution of the covariates in the two groups to reduce this bias; for example, using matching or subclassification, sometimes in combination with model-based adjustment. To estimate propensity scores, which are the conditional probabilities of being treated given a vector of observed covariates, we must model the distribution of the treatment indicator given these observed covariates. Much work has been done in the case where covariates are fully observed. We address the problem of calculating propensity scores when covariates can have missing values. In such cases, which commonly arise in practice, the pattern of missing covariates can be prognostically important, and ...

Looking Into the Black Box: A Survey of the Matching Function

Abstract: We survey the microfoundations, empirical evidence and estimation issues underlying the aggregate matching function. Several microeconomic matching mechanisms have been suggested in the literature with some successes but none is generally accepted as superior to all others. Instead, an aggregate matching function with hires as a function of vacancies and unemployment has been successfully estimated for several countries. The Cobb-Douglas restrictions with constant returns to scale perform well. Recent work has utilized disaggregated data to go beyond aggregate estimates, with many refinements and suggestions for future research.

The Dynamics of Reorganization in Matching Markets: A Laboratory Experiment Motivated by a Natural Experiment

Abstract: We create an environment in which congestion forces agents to match inefficiently early. We then introduce one of two centralized clearinghouse mechanisms. One of these has been successfully used to halt this kind of unraveling in a number of labor markets, while the other has failed. When it is costlyfore rms and workers to be mismatched compared with the costs of matching early, the experimental observations reproduce the e eld observations. Furthermore, the experiment permits us to observe the transition between a decentralized and a centralized market, both when the centralized market fails to control unraveling and when it succeeds, at a level of detail unavailable in e eld data.

An Evaluation of Public Sector Sponsored Continuous Vocational Training Programs in East Germany

Abstract: This study analyses the effect of public sector sponsored continuous vocational training and retraining in East Germany after unification with West Germany in 1990. It presents estimates of the average gains from training participation in terms of earnings, employment probabilities and career prospects after the completion of training. The data is from the German Socio-Economic Panel (GSOEP, 1990-1994). The GSOEP allows to observe individual behaviour on a monthly, respectively yearly, basis. The results suggest that despite public expenditures of more than DM 25 bn (1991 to 1993), there are no positive effects in the first year after training, but that participants expect positive effects over a longer time horizon. The latter however is beyond the sampling period.

The Determinants of Equilibrium Unemployment

Abstract: The paper takes the search and matching model of the aggregate labor market to the data. It tests the model's empirical validity and employs structural estimation to generate a characterization of the optimal behavior of firms and workers. The model is applied to Israeli data that are uniquely suited for this kind of empirical investigation. The structural estimates are used to quantify the frictions embodied in the model, including the costs of search, the congestion and trading externality effects, and the matching process. A calibration-simulation analysis then studies the effect of several key variables on equilibrium unemployment.

Substantial Gains in Bias Reduction from Matching with a Variable Number of Controls

Abstract: In observational studies that match several controls to each treated subject, substantially greater bias reduction is possible if the number of controls is not fixed but rather is allowed to vary from one matched set to another In certain cases, matching with a fixed number of controls may remove only 50% of the bias in a covariate, whereas matching with a variable number of controls may remove 90% of the bias, even though both control groups have the same number of controls in total An example of matching in a study of surgical mortality is discussed in detail

Natural language search method and apparatus, including linguistically-matching context data

Abstract: A method and apparatus for performing a search for information containing natural language is disclosed which uses a natural language query. The query is input in the form of units of the natural language and this is matched with units in the natural language of the data. Where there are unmatched units in the query and/or the data, context data in the form of one or more unmatched units of the query and/or the data is generated. Each unmatched unit as a predefined linguistic relationship to one of the or each matched unit. Output data is formed as matched units with any respective context data.

Language recognition using a similarity measure

Abstract: A dynamic programming technique is provided for matching two sequences of phonemes both of which may be generated from text or speech. The scoring of the dynamic programming matching technique uses phoneme confusion scores, phoneme insertion scores and phoneme deletion scores which are obtained in advance in a training session and, if appropriate, confidence data generated by a recognition system if the sequences are generated from speech.

Feminist participatory action research: methodological and ethical issues

Abstract: Close relationships between researchers and participants engaged in a feminist participatory action research project have brought joy and insight, but also challenges Through the project we collaborate to enhance participants' careers and, among some, develop feminist consciousness In this paper we discuss methodological and ethical issues that derive from the closeness of the relationships between many of the participants and ourselves We explore our subjectivities, the issues associated with interpreting participants' stories, actions and conversations, the risk of perpetuating uncritical assimilation or colonisation for Maori participants, and the challenge of matching practice with ideals of emancipation for all women

Effective information retrieval using genetic algorithms based matching functions adaptation

Abstract: Knowledge intensive organizations have vast array of information contained in large document repositories. With the advent of E-commerce and corporate intranets/extranets, these repositories are expected to grow at a fast pace. This explosive growth has led to huge, fragmented, and unstructured document collections. Although it has become easier to collect and store information in document collections, it has become increasingly difficult to retrieve relevant information from these large document collections. This paper addresses the issue of improving retrieval performance (in terms of precision and recall) for retrieval from document collections. There are three important paradigms of research in the area of information retrieval (1R): Probabilistic IR, Knowledge-based IR, and, Artificial Intelligence based techniques like neural networks and symbolic learning. Very few researcher have tried to use evolutionary algorithms like genetic algorithms (GAs). Previous attempts at using GAs have concentrated on modifying document representations or modifying query representations. This work looks at the possibility of applying GAs to adapt various matching functions. It is hoped that such an adaptation of the matching functions in lead to a better retrieval performance than that obtained by using a single matching function. An overall matching function is treated as an weighted combination of scores produced by individual matching functions. This overall score is asked to rank and retrieve documents. Weights associated with individual functions are searched using Genetic Algorithms. The idea is tested on a real document collection called the Cranfield collection. The results look very encouraging.

Empirical Matching Functions: Estimation and Interpretation Using State-Level Data

Abstract: Using quarterly data to estimate state-level matching functions, we obtain point estimates that are slightly higher than are found with national gross flows data, likely because of inherent differences in the data sources. We also estimate matching functions separately by the source of the new hire, and show that the results are consistent with the assumptions of endogenous job search by the employed and a preference for employed applicants by firms. Thus, care must be taken in interpreting empirical matching functions, which are likely a reduced-form combination of a structural matching function and a job competition model.

Information processing system

Abstract: The menu displays of a base-station device and its data-correlated, portable device are managed. In the base-station device, first icon information corresponding to the menu is displayed on a first display screen. In the portable device, second icon information (corresponding to the first) is displayed on a second display screen. The base-station device has a first storage unit for storing the first icon information, a first display control unit for controlling a first display unit, and a first communication unit for communicating with the portable device. The portable device has a second storage unit for storing the second icon information, a second display control unit for controlling a second display unit, and a second communication unit for communicating with the base-station device and for matching pieces of display data stored in the first and second storage units. Thus, the size of the second icon information is maintained smaller than the size of the first.

Motor constraints on the development of perception-action matching in infant reaching

Abstract: Previous studies on reaching and grasping have suggested that infants need considerable experience at both seeing and touching in order to develop responses adapted to the environment. Such an account, however, does not reveal how appropriate perception-action matching emerges from these repeated experiences at seeing and touching. The present research addresses this issue by investigating the dynamics of perceiving and acting in 5- to 9-month-old infants as they saw, reached for, touched, and grasped objects of different sizes and texture. To gain insights into the mechanisms of change that underlie pattern formation, we observed infants’ responses as a function of time, as infants reached for and manipulated objects successively. We found that the developmental process by which appropriate perception-action matching emerges is tied to important changes in the motor system. Before 8 months, infants’ reaching responses are constrained by systemic motor tendencies that conflict with the process of perceptual-motor mapping. When these motor tendencies disappear, infants are able to use and integrate visual and haptic information to scale their actions to objects. These results are consistent with a dynamic systems approach, which views behavioral changes and their underlying psychological processes as the product of continuous tensions and interactions between the organism’s own constraints and the characteristics of the task at hand.

Looking into the Black Box: A Survey of the Matching Function

Abstract: We survey the microfoundations, empirical evidence and estimation issues underlying the aggregate matching function. Several microeconomic matching mechanisms have been suggested in the literature with some successes but none is generally accepted as superior to all others. Instead, an aggregate matching function with hires as a function of vacancies and unemployment has been successfully estimated for several countries. The Cobb-Douglas restrictions with constant returns to scale perform well. Recent work has utilized disaggregated data to go beyond aggregate estimates, with many refinements and suggestions for future research.

Aggregation in Matching Markets

Abstract: This article develops aggregate relations for a matching market of heterogeneous suppliers and demanders. Under particular assumptions about the distribution of preferences and the matching game, asymptotic aggregate relations for the number of realized matches of different types in the presence of flexible contracts (such as a price) are derived. Simulation experiments demonstrate that the model also provides excellent predictions in small populations. The potential for applications within demographic, labor market, and welfare analyses is discussed.

An information statistical approach to the modifiable areal unit problem in incidence rate maps

Abstract: The modifiable areal unit problem becomes apparent when incidence rates are mapped on the basis of areal units. Although small units with high spatial accuracy can present unreliable rates, large spatial units may remove relevant geographical variation. Regarding mapping as a kind of statistical modelling, this author proposes a new methodology to select appropriate areal units using the Akaike information criterion and two search methods for an informative geographical aggregation in map construction. The optimal zoning of similarity is suitable for finding spatial anomalies but presents a biased overall pattern. An alternative approach is to cluster areal units according to explanatory variables: this shows clear spatial patterns of elderly men's mortality matching the ecological structure in the Tokyo metropolitan area.

The Hospitals/Residents Problem with Ties

Abstract: The hospitals/residents problem is an extensively-studied many-one stable matching problem. Here, we consider the hospitals/ residents problem where ties are allowed in the preference lists. In this extended setting, a number of natural definitions for a stable matching arise. We present the first linear-time algorithm for the problem under the strongest of these criteria, so-called super-stability. Our new results have applications to large-scale matching schemes, such as the National Resident Matching Program in the US, and similar schemes elsewhere.

Efficient Matching for Web-Based Publish/Subscribe Systems

Abstract: There is a need for systems being able to capture the dynamic aspect of the web information by notifying users of interesting events. Content-based publish/subscribe systems are an emerging type of publish/subscribe systems where events are filtered according to their attribute values, using filtering criteria defined by the subscribers, and then sent to the interested subscribers. Compared to traditional publish/subscribe systems, content-based systems offer more subscription expressiveness. The cost of this gain in expressiveness is an increase in the complexity of the matching process: the more sophisticated the constructs, the more complex the matching process. In this paper, we present an efficient and scalable solution to the matching problem. We also present a semi-structured event model which is well suited for the information published on the Web, and flexible enough to support easy integration of publishers.

Least-Squares Matching with Airborne Laserscanning Data in a TIN Structure

Abstract: A number of tasks in airborne laserscanning require the establishment of correspondences between point data from neighbouring strips, or referencing between point clouds and object models. These tasks may be solved by interpolating laserscanner data, which are usually irregularly distributed 2 1 /2-D points, to a regular grid and applying standard photogrammetric matching techniques. Instead, the paper presents a formulation of least squares matching based on the original data points in a triangulated irregular network structure, thus avoiding degrading effects caused by the interpolation. The technique determines shifts in all three coordinate directions together with their covariance matrix. It can be shown that applying matching techniques to laserscanner data causes large systematic errors of the shift parameters in the case of partial occlusions. The presented formulation on the basis of a TIN structure allows for manifold extensions to solve this problem. The technique and a number of extensions have been implemented and applied to the measurement of strip errors in an airborne laser scanner dataset with moderate point density, consisting of 20 strips including crossing strips. The paper shows the results from this test, discusses the advantages of the presented technique and the limitations of matching techniques applied to laserscanner data. Special attention has to be paid to problems caused by height discontinuities in the data and by the fact that the design matrix in least squares matching is derived from observations with stochastic properties. The latter leads to precision figures that are usually much too optimistic. A detailed analysis of the design matrix and extensive testing lead to better funded precision figures for the standard deviation of the obtained shift parameters. These are in the order of one centimeter in height direction and one decimeter in horizontal direction, corresponding to about 1 /20th of the average point spacing.