Showing papers on "Matching (statistics) published in 1992"

Robust Model-based Motion Tracking Through the Integration of Search and Estimation

Abstract: A computer vision system has been developed for real-time motion tracking of 3-D objects, including those with variable internal parameters. This system provides for the integrated treatment of matching and measurement errors that arise during motion tracking. These two sources of error have very different distributions and are best handled by separate computational mechanisms. These errors can be treated in an integrated way by using the computation of variance in predicted feature measurements to determine the probability of correctness for each potential matching feature. In return, a best-first search procedure uses these probabilities to find consistent sets of matches, which eliminates the need to treat outliers during the analysis of measurement errors. The most reliable initial matches are used to reduce the parameter variance on further iterations, minimizing the amount of search required for matching more ambiguous features. These methods allow for much larger frame-to-frame motions than most previous approaches. The resulting system can robustly track models with many degrees of freedom while running on relatively inexpensive hardware. These same techniques can be used to speed verification during model-based recognition.

Estimating exposure effects by modelling the expectation of exposure conditional on confounders

Abstract: In order to estimate the causal effects of one or more exposures or treatments on an outcome of interest, one has to account for the effect of "confounding factors" which both covary with the exposures or treatments and are independent predictors of the outcome. In this paper we present regression methods which, in contrast to standard methods, adjust for the confounding effect of multiple continuous or discrete covariates by modelling the conditional expectation of the exposures or treatments given the confounders. In the special case of a univariate dichotomous exposure or treatment, this conditional expectation is identical to what Rosenbaum and Rubin have called the propensity score. They have also proposed methods to estimate causal effects by modelling the propensity score. Our methods generalize those of Rosenbaum and Rubin in several ways. First, our approach straightforwardly allows for multivariate exposures or treatments, each of which may be continuous, ordinal, or discrete. Second, even in the case of a single dichotomous exposure, our approach does not require subclassification or matching on the propensity score so that the potential for "residual confounding," i.e., bias, due to incomplete matching is avoided. Third, our approach allows a rather general formalization of the idea that it is better to use the "estimated propensity score" than the true propensity score even when the true score is known. The additional power of our approach derives from the fact that we assume the causal effects of the exposures or treatments can be described by the parametric component of a semiparametric regression model. To illustrate our methods, we reanalyze the effect of current cigarette smoking on the level of forced expiratory volume in one second in a cohort of 2,713 adult white males. We compare the results with those obtained using standard methods.

Evaluating investments in IT

Abstract: Evaluating the costs and benefits of IT projects is currently a major issue for senior general managers. This paper focuses on a particular aspect of the problem: how organizations appraise IT investments in taking the decision whether to go ahead with them or not. The paper looks first at the different roles of evaluation; second at what is done in practice and third at what might be done given the wide range of techniques that are available and the widely different circumstances in which appraisal is undertaken. A speculative heuristic is proposed for matching an evaluation method with a particular situation. The method is presented in the hope of stimulating further research into the matching problem.

Characterizing the effect of matching using linear propensity score methods with normal distributions

Abstract: SUMMARY Matched sampling is a standard technique for controlling bias in observational studies due to specific covariates. Since Rosenbaum & Rubin (1983), multivariate matching methods based on estimated propensity scores have been used with increasing frequency in medical, educational, and sociological applications. We obtain analytic expressions for the effect of matching using linear propensity score methods with normal distributions. These expressions cover cases where the propensity score is either known, or estimated using either discriminant analysis or logistic regression, as is typically done in current practice. The results show that matching using estimated propensity scores not only reduces bias along the population propensity score, but also controls variation of components orthogonal to it. Matching on estimated rather than population propensity scores can therefore lead to relatively large variance reduction, as much as a factor of two in common matching settings where close matches are possible. Approximations are given for the magnitude of this variance reduction, which can be computed using estimates obtained from the matching pools. Related expressions for bias reduction are also presented which suggest that, in difficult matching situations, the use of population scores leads to greater bias reduction than the use of estimated scores.

Tree Matching Problems with Applications to Structured Text Databases

Abstract: A venturi scrubber for the scrubbing of an inlet gas stream with a scrubbing liquid or slurry, to remove gaseous or vaporous components from the gas stream, or to remove entrained solid particulate or discrete liquid droplet (fog or mist) constituents, and thereby to prevent air pollution and/or to recover the component or constituent. The venturi scrubber has an adjustable throat characterized by the provision of structure to adjust the cross-sectional dimension of the gas passage at or adjacent to the throat section. The structure includes at least one movable baffle at the periphery of the gas passage, and a container. The container is disposed external to and contiguous with the baffle, and a controlled amount of a fluid is passed into the container so that the internal fluid pressure within the container, and resultant volumetric dimension of the container, and thereby also the resultant displacement of the baffle relative to the periphery of the throat section, are adjustable in proportion to a change in the flow rate of the inlet gas stream.

Urban Structure and the Labour Market: Worker Mobility, Commuting, and Underemployment in Cities

Abstract: Theory of urban spatial structure information, search and matching - a survey job-worker matching in urban space job-worker matching and urban commuting job-worker matching and underemployment employment policies and urban redevelopment final thoughts...for now.

Reasoning with conditionals containing negated constituents.

Abstract: Three experiments investigated matching bias in conditional reasoning tasks. Matching bias occurs when Ss ignore negations and match named items. Experiment 1 used an abstract and a thematic version of Evans's (1972) construction task. Results showed that matching may be due to an interaction between task demands and constructing contrast classes when interpreting negations. Experiment 2, which used Wason's (1968) selection task, introduced a manipulation to ease contrast-class construction. Confirmation plus falsification dominated over matching. Experiment 3 introduced two other manipulations to aid contrast-class construction with abstract material. Confirmation was facilitated, matching was suppressed, and falsification remained unchanged. These results suggest that matching occurs only when insufficient or ambiguous information prevents the intended interpretation of negations.

Performance evaluation of scene registration and stereo matching for cartographic feature extraction

Abstract: Three major areas in the development of competent 3-D scene interpretation system are discussed. First, the importance of accurate automatic scene registration and the difficulty in automated extraction and matching of scene reference points are described. Second, the authors describe two stereo matching algorithms, S1, which is an area-based matcher previously used in the SPAM system, and S2, which is a feature-based matching algorithm based on hierarchical waveform matching. Third, the authors introduce several performance evaluation metrics that made it possible to measure the quality of the overall scene recovery, the building disparity estimate, and the quality and sharpness of the building delineations. Such manually generated scene reference models are critical for understanding strengths and weaknesses of various matching algorithms and in the incremental development of improvements to existing algorithms. Experiments were performed on difficult examples of aerial imagery. >

A Taxonomy of Automated Trade Execution Systems

Abstract: A taxonomy of existing and planned automated trade execution systems in financial markets is provided. Over 50 automated market structures in 16 countries are analyzed. The classification scheme is organized around the principle that such markets consist of an algorithm that performs a trade matching function, together with information display and transmission mechanisms. Automated market structures are classified by ordered sets of trade execution priority rules, trade matching protocols and associated degree of automation of price discovery, and transparency, to include informational asymmetries between classes of market participants. Systematic differences in systems across types of financial instruments, geographical market centers, and over time are analyzed.

Getty's Synoname™ and its cousins: A survey of applications of personal name-matching algorithms

Abstract: The study reported in this article was commissioned by the Getty Art History Information Program (AHIP) as a background investigation of personal name-matching programs in fields other than art history, for purposes of comparing them and their approaches with AHIP's Synoname™ project. We review techniques employed in a variety of applications, including art history, bibliography, genealogy, commerce, and government, providing a framework of personal name characteristics, factors in selecting matching techniques, and types of applications. Personal names, as data elements in information systems, vary for a wide range of legitimate reasons, including cultural and historical traditions, translation and transliteration, reporting and recording variations, as well as typographical and phonetic errors. Some matching applications seek to link variants, while others seek to correct errors. The choice of matching techniques will vary in the amount of domain knowledge about the names that is incorporated, the sources of data, and the human and computing resources required. Personal name-matching techniques may be included in name authority work, information retrieval, or duplicate detection, with some applications matching on name only, and others combining personal names with other data elements in record linkage techniques. We discuss both phonetic- and pattern-matching techniques, reviewing a range of implemented and proposed name-matching techniques in the context of these factors. © 1992 John Wiley & Sons, Inc.

Authorization matching system

Abstract: An authorization matching system for a credit card transaction system assigns the same identification code to authorization and transaction records associated with a particular transaction. The records may be matched by matching the identification number in the records, even if other data in the records does not match.

Smoothing and Matching of 3-D Space Curves

Abstract: We present a new approach to the problem of matching 3D curves. The approach has an algorithmic complexity sublinear with the number of models, and can operate in the presence of noise and partial occlusions.

Teaching arbitrary matching via sample stimulus-control shaping to young children and mentally retarded individuals: a methodological note.

Abstract: Two experiments demonstrated the efficacy of sample stimulus-control shaping programs for teaching arbitrary matching to 4 subjects who did not acquire the performances via standard methods (i.e., differential reinforcement and, in two cases, comparison intensity fading). All 4 had previously demonstrated identity matching with two-dimensional forms. Identity matching performances were then transformed into arbitrary matching by gradually changing the sample stimuli until they no longer resembled the comparison stimuli. Where applicable, these methods may have advantages over others that have been used after the failure of standard techniques.

Chapter 16 Two-sided matching

Abstract: Publisher Summary This chapter discusses the games that are two-sided matching markets. The phrase two-sided refers to the fact that agents in such markets belong, from the outset, to one of two disjoint sets-e.g, firms or workers. The term matching refers to the bilateral nature of exchange in these markets. The game-theoretic analysis of these markets has proved useful in various empirically oriented studies. This chapter describes some of the phenomena the theory should be able to explain, and concludes by returning to consider how the theory addresses the empirical questions raised at the beginning. The chapter focuses on both the core of the game and the dominant and equilibrium strategies under various rules about how the game might be played. The distinction between cooperative and noncooperative game theory is often somewhat artificial because the tools of both kinds of theory can be used to study the same phenomena.

Nonlinear pattern matching in trees

Abstract: Tree pattern matching is a fundamental operation that is used in a number of programming tasks such as mechanical theorem proving, term rewriting, symbolic computation, and nonprocedural programming languages. In this paper, we present new sequential algorithms for nonlinear pattern matching in trees. Our algorithm improves upon know tree pattern matching algorithms in important aspects such as time performance, ease of integration with several reduction strategies and ability to avoid unnecessary computation steps on match attempts that fail. The expected time complexity of our algorithm is linear in the sum of the sizes of the two trees.

An Analysis of Generalized Identity Matching-to-Sample Test Procedures

Abstract: This paper examines issues that must be considered when evaluating generalized identity matching to sample. We suggest that (a) stimuli displayed together on tests of generalized identity matching should have comparable experimental histories, and (b) identity matching procedures should be differentiated as either “conditional” or “nonconditional,” depending upon whether or not conditional discrimination is required. Although either type of procedure might be adequate for demonstrating a “matching concept,” we suggest that only generalized conditional identity matching provides an adequate test for the reflexive property of conditional relations.

Efficient Boolean function matching

Abstract: Efficient algorithms for performing the matching step in technology mapping are proposed. The main result is an algorithm for matching under input negations that takes time polynomial in the size of the BDDs representing the functions to be matched. This algorithm is the basis for efficient methods for matching under permutations, bridging and constant inputs. A simple mapper based on the algorithms was implemented and tested on a suite of combinational circuits. Using the Actel type 1 mother cell, the mapper required an average of 8.5% fewer cells than mispga. When integrated into a more sophisticated technology mapper, the matching algorithms could provide even better performance. >

Alphabet independent two dimensional matching

Abstract: Alphabet Independent Two Dimensional Matching Amihood Amir* Gary Bensont Martin Farach$ Georgia Tech Univ. of Maryland DIMACS There are many solutions to the string matching pmZllem whkh are strictly linear in the input size and independent ofalphabet.size. Furthermore, the model of computation for these algorithms is very weak: they allow only simple arithmetic and comparisons of equality between characters of the input. In contrast, algorithm for two dimensional matching have needed stronger models of computation, most notably assuming a totally ordered alphabet. The fastest algorithms for two dimensional matching have therefore had a logarithmic dependence on the alphabet size. In the worst case, this givea an algorithm that runs in 0(n2 log m) with 0(rn2 log m) preprocessing. We show an algorithm for two dimensional matching with an 0(n2) text scanning phase. Furthermore, the text scan requires no special assumptions about the alphabet, i.e. it runs on the same model as standard linear time string matching algorithm. the *College of Computing, Georgia Institute of Technology, Atlanta, GA 30332-0280; (404) 853-0083; amir@cc.gatecb. edu; Partially supported by NSF ~ant IR.I-90-13055. tDept. of Computer Scienee, University of Maryland, College Park, MD 20742; (301) 405-2715; benaon@cs.umd.edq Partially supported by NSF grant IRI-90-13055. :DIMACS, Box 1179, Rutgers University, Piscataway, NJ 08855; (808) 932-592% farach@Xhu.acs.mtgers.edw, Supported by DIMACS under NSF contract STC-88-09648. Permission to copy without fee all or pert of thie material ie grantad provided that tha copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and ite date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or apacific permission. 24th ANNUAL ACM STOC 5/92/VICTORIA, B.C., CANADA a 1992 ACM 0-89791-51 2-7/9210004/0059 ...$1 .50

Theory of single and multiple interfaces : the method of surface Green function matching

Abstract: Technical preliminaries general form of the surface Green function matching (SGFM) analysis matching analysis for continuous systems matching for discrete systems SGFM for coupled interfaces the geometry of the matching surface the full transfer matrix and SGFM for continuous media transfer matrix and SGFM for discrete media a miscellany of physical problems some Hamiltonians commonly used for matching calculations.

“thin” versus “thick” matching in the mantel-haenszel procedure for detecting dif

Abstract: This Monte Carlo study examined strategies for forming the matching variable for the Mantel-Haenszel DIF procedure; “thin” matching on total test score was compared to forms of “thick” matching, pooling levels of the matching variable. Data were generated using a three-parameter item response theory model with common guessing parameter. Number of subjects and test length were manipulated, as were the difficulty, discrimination, and presence/absence of DIF in the studied item. Outcome measures were the transformed log-odds ΔMH, its standard error, and the MH chi-square statistic. For short tests (5 or 10 items), thin matching yielded very poor results, with a tendency to falsely identify items as possessing DIF against the reference group. The best methods of thick matching yielded outcome measure values closer to the expected value for non-DIF items, and a larger value than thin matching when the studied item possessed DIF. Intermediate length tests yielded similar results for thin matching and the best methods of thick matching. The method of thick matching that performed best depended upon the measure used to detect DIF. Both difficulty and discrimination of the studied item were found to have a strong effect on the value of ΔMH.

A global approach for least-squares image matching and surface reconstruction in object space

Abstract: The automatic determination of corresponding points in digital, images, called digital image matching , is one of the key factors limiting complete automation in photogrammetry. In recent research work at different institutions a tendency has been observed for performing digital image matching on a global scale and in object space. In view of these facts, a general model for digital photogrammetry, developed over the last three years and integrating area-based multi-image matching, point determination, object surface reconstruction, and orthophoto generation into one model only, is presented in this paper.

Research on matching alcoholic patients to treatments: findings, issues, and implications.

Abstract: No single treatment has emerged as effective for all persons diagnosed as alcoholics. "Patient-treatment matching" is a method of choosing between alternative treatment options based on particular patient characteristics that interact differentially with interventions to produce more beneficial results than if "matching" had not been done. This review distinguishes three models for interactions between patient characteristics and interventions in terms of their clinical implications. Supporting empirical evidence for matching is also summarized. Requirements for the future research agenda are discussed and the pros and cons of implementing patient treatment matching in the clinical setting are addressed.

Efficient Randomized Dictionary Matching Algorithms (Extended Abstract)

Abstract: The standard string matching problem involves finding all occurrences of a single pattern in a single text. While this approach works well in many application areas, there are some domains in which it is more appropriate to deal with dictionaries of patterns. A dictionary is a set of patterns; the goal of dictionary matching is to find all dictionary patterns in a given text, simultaneously.