bluuebunny/crossref_metadata_2025 huggingface dataset:
Very low bit rate speech coding based on HMMs
Authors: Hiroi Jun , Tokuda Keiichi , Masuko Takashi , Kobayashi Takao , Kitamura Tadashi
Published: August 2002

In this paper the authors describe very low bit rate speech coding based on HMMs (Hidden Markov Models). In the coder, phoneme recognition is performed using HMMs, then the phoneme index array, state duration length, and pitch information are sent to the decoder. In the decoder, the phoneme HMMs are linked in accordance with the phoneme index array. Then, a mel‐cepstral array is generated from the linked HMMs based on a speech parameter generation algorithm using likelihood maximization standards in accordance with the state duration length. Finally, speech is synthesized by exciting an MLSA (Mel Log Spectrum Approximation) filter with the generated mel‐cepstral as a coefficient in accordance with the pitch information. The results of subjective evaluation experiments show that performance similar to a vocoder based on 400 bit/s (8 bit/frame × 50 frame/s) vector quantization excluding pitch information can be obtained using the proposed format at 146 bits/s (including a 26% silent interval) excluding pitch information. © 2001 Scripta Technica, Syst Comp Jpn, 32(12): 38–46, 2001
Introducing the fisheye view into graph drawing algorithm
Authors: Nagumo Jun , Tanaka Jiro
Published: August 2002

In this paper, an algorithm is proposed for automatic drawing of undirected graphs. Specifically, a modified method of introducing a fisheye view into the force‐directed redrawing algorithm is offered. The proposed representation involves enlargement of regions located near specified nodes and contraction of far regions by varying the edge length while not using node position data, which ensures easy incorporation into the conventional force‐directed rearrangement technique. In addition, smooth display of graph transformations using the results of subsequent iterative calculation, which is a feature of the force‐directed algorithm, is maintained. © 2001 Scripta Technica, Syst Comp Jpn, 32(12): 60–66, 2001
Improvement of imaging speed in fluorescent x‐ray computed tomography using synchrotron radiation
Authors: Hasegawa Yasuhiro , Yu Quanwen , Noto Daisuke , Takeda Tohoru , Hyodo Kazuyuki , Yashiro Toru , Yuasa Tetsuya , Hiranaka Yukio , Itai Yuji , Akatsuka Takao
Published: August 2002

Improving the speed of fluorescent X‐ray CT imaging using synchrotron radiation has been studied from the points of view of the imaging system and the processing algorithm. Regarding the imaging system, high‐speed imaging at 2 seconds per point with a dead time of about 6% has been realized by incorporating an electronic system which operates stably in the high count rate region. In addition, the amounts of computation and memory required have been reduced to about 1/100 of the levels realized up to now by improving the efficiency of the reconstruction algorithm. The quantitative properties of this system have been confirmed by tests with a physical phantom and the iodine distribution has been estimated in in vitro human thyroid images. These results indicate the implementability of in vivo fluorescent X‐ray CT instrumentation. © 2002 Scripta Technica, Syst Comp Jpn, 33(2): 1–11, 2002
A study on schema preservation by crossover
Authors: Yamamoto Kimihiro , Naito Shozo
Published: August 2002

This paper considers the combinatorial optimization problem in which the solution (sample) can be decomposed linearly into multiple schemata. Focusing on an arbitrary kind of schema, the schema preservation mechanism of the crossover in the genetic algorithm is discussed from the viewpoint of the increase or decrease of the number of samples (considered samples) containing the considered schema in the set of sample bit strings. It is shown that the change in the number of considered samples with time is divided into two kind of phases (stable and unstable phases), depending on whether or not there exists a point of equilibrium for increase and decrease in copying during the course of selection, and for degradation by destruction in crossover and mutation. It is shown that the transition between the stable phase and the unstable phase occurs according to the magnitude relation between the average fitness of the considered samples and the average fitness of the whole set of sample bit strings. By setting the crossover ratio as a higher value in the genetic algorithm, the schema is uniformly embedded in the whole set of sample bit strings, which increases the average fitness of the considered samples, and generates an equilibrium point that maintains a constant number of considered samples. Lastly, a computer simulation is performed, and it is shown that the discussion of the schema preservation mechanism of the crossover is adequate. © 2002 Scripta Technica, Syst Comp Jpn, 33(2): 64–76, 2002
A web page transmission mechanism with transmission order control of inline objects
Authors: Nakano Tadashi , Harumoto Kaname , Shimojo Shinji , Nishio Shojiro
Published: August 2002

Due to the increasing popularity of the Internet, the WWW (World Wide Web) has become the most popular way to distribute multimedia contents. In the WWW, impressive information can be provided by embedding a large number of inline objects such as images in a WWW page. Since these inline objects are generally presented in WWW browsers in transmission order, the transmission order of inline objects becomes very important, especially for users accessing the Internet with a low‐speed connection such as a dial‐up line. In this paper, we propose a page transmission mechanism, which allows content authors to specify the transmission order of inline objects in WWW pages. First, we define a language to specify the transmission order of inline objects based on XML (Extensible Markup Language). We then discuss how we can implement the transmission order control, and propose a new protocol, HTSP (Hypertext Streaming Protocol), which realizes efficient transmission of ordered inline objects. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(4): 14–24, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1116
Bookmark‐agent: Sharing of bookmarks for search assists
Authors: Mori Mikihiko , Yamada Seiji
Published: August 2002

The Bookmark‐Agent is a system which references bookmark files that register URLs which users are interested in, and then shares information among users. This engine can perform information searches more effectively than existing search engines. When a user is searching for a Web page by browsing, the agent searches for Web pages thought to represent what the user wants from among bookmarks, then presents a list in hyperlink form to the user's browser. In addition, the agent can also search other users' bookmarks by communicating with other users' agents. By using this agent in a small‐scale group consisting of users with similar interests, information which has been filtered by users, that is, bookmarks, can be used. As a result, the Bookmark‐Agent can display Web pages with a precision level higher than that of existing search engines. This is confirmed by experiments using six users for the purpose of evaluating the performance of the Bookmark‐Agent. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(4): 69–76, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1121
Fast reconstruction of three‐dimensional images in Fresnel transform imaging technique using optical imaging system
Authors: Ito Satoshi , Kawaharada Shingo , Kamimura Yoshitsugu , Yamada Yoshifumi
Published: August 2002

In this paper, a fast reconstruction of three‐dimensional images, based on the analogy between the expression for the NMR signal in the three‐dimensional Fresnel transform NMR imaging and the expression for light diffraction, is presented. When three‐dimensional imaging is applied to MRI, the problem arises that the computation time for reconstruction is too long, due to the large amount of data. However, the reconstruction time for the spatially continuous cross‐sectional images can be greatly reduced by high‐speed optical operation if the signal is sent to a liquid‐crystal spatial light modulator as a set of Fresnel hologram signals, to be displayed continuously and illuminated by coherent light. In this study, holographic reconstruction is applied to image reconstruction in three‐dimensional Fresnel transform imaging, and an attempt is made to improve the speed of image reconstruction by high‐speed transfer of the obtained signals to the holographic reconstruction system as a set of Fresnel holograms. Thus, the MR cross‐sectional image is reconstructed with the video rate from the three‐dimensional signal data. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(5): 21–29, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1124
Vocal tract length normalization using rapid maximum‐likelihood estimation for speech recognition
Authors: Emori Tadashi , Shinoda Koichi
Published: August 2002

Speaker normalization techniques for correcting differences in the vocal tract lengths of different speakers, referred to as vocal tract length normalization, in a large vocabulary voice recognition system using a hidden Markov model (HMM), have been proposed in recent years. In this paper, a scheme for approximating especially small changes in the vocal tract length by linear mapping using a vocal tract length parameter in cepstrum space and maximum‐likelihood estimation of this parameter from vocalization is proposed. The proposed method can estimate a more optimal parameter for a speaker with a small amount of computation than in past schemes using multiple vocal tract length parameters in advance. In evaluation tests of the recognition of 5000 single Japanese words, the proposed scheme decreased errors by 7.1% alone and 14.6% in combination with cepstrum mean normalization (CMN). © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(5): 30–40, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1125
Modeling collaborations among objects that change their roles dynamically and its modularization mechanism
Authors: Naoyasu Ubayashi , Tetsuo Tamai
Published: August 2002

For the representation of the collaborative operations among objects (computational entities), many of the techniques proposed at present treat the collaborative operations only as the concept in analysis and design stages; moreover, the roles carried by the respective objects have the problem of being fixed from the beginning to the end. Based on the environment‐adaptive computation model “ϵ” computation proposed by the authors, in this paper we will study from the language side a description method for the case of collaborative operations in which the group of objects changes their roles dynamically along with the progress of computation. Furthermore, we will present a method for defining the collaborative operations among objects as general collaboration protocol components and reuse them again. ϵ computation is a model in which the field where the group of objects operates collaboratively is considered as an environment for the individual objects; the object can change its roles and collaboration forms with other objects dynamically by entering the environment or leaving the environment. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(5): 51–63, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1127
Classification of nerve action potentials for estimation of sensory unit activity
Authors: Nakatani Hironori , Watanabe Takashi , Ohba Shigeo , Hoshimiya Nozomu
Published: August 2002

A method for classifying action potentials to estimate a sensory unit activity was developed. The classification of action potentials based on their waveforms involves a pattern classification problem without supervised signal. Some methods depended on an operator for specifying parameters due to the lack of a standard criterion for classification. Therefore, we have proposed an objective classification method in this paper. The performance of our method was evaluated with a simulated signal generated by a peripheral nerve model. Our method provided more appropriate classification results against the influence of the noise process than the conventional method whose reliability was reported to be high in previous studies. The classification results of our method applied to the cuff recordings suggested that there were several different stretch receptors of different characteristics, which agrees with previous reports. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(6): 44–52, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1131
Pitch pattern generation using multispace probability distribution HMM
Authors: Masuko Takashi , Tokuda Keiichi , Miyazaki Noboru , Kobayashi Takao
Published: August 2002

A scheme for simultaneously modeling and generating a pitch pattern and a spectral sequence on the basis of a hidden Markov model (HMM) is presented. Since a pitch pattern is expressed as a time series of voiced intervals taking continuous values and voiceless intervals without values, it cannot be modeled by the usual HMM. This paper proposes a scheme for modeling a pitch and a spectrum integrally with characteristic parameters that combine pitch parameters and spectral parameters by applying an HMM based on a multispace probability distribution (multispace probability distribution HMM: MSD‐HMM). In addition, a context clustering scheme based on decision trees in the MSD‐HMM is derived, and a scheme for constructing the model while taking account of the variation factors of the pitch and the spectrum is presented. In addition, it is shown that pitch patterns and spectral sequences approximating real voice can be generated by using the parameter generation scheme based on the maximum likelihood criterion. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(6): 62–72, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1133
Video corpus construction and analysis
Authors: Satou Takashi , Kojima Haruhiko , Akutsu Akihito , Tonomura Yoshinobu
Published: August 2002

In this paper, we propose a method of handling videos based on the construction and analysis of a video corpus containing a large volume of video data and attributes. A video corpus was constructed by coding videos of a total length of approximately 180 hours by the MPEG‐2 standard and adding attributes, such as automatically extracted characteristic values and manually entered information. These attributes include, among other things, such items as cut points, camera operation, scene change techniques, captions placed by a television opaque projector, and scaled down images. The video corpora provide tools for the input, analysis, retrieval, and visualization of data and characteristic values, allowing for structuring in a distributed environment, thus enhancing their usability. We also demonstrate the use of InfoStripes, a tool intended for the visualization of videos, whose total length can amount to several hundred hours, in the form of stripes. In conclusion, as a preliminary analysis of the video corpus, we extracted common sequences usingn‐grams of frame images and analyzed the distribution of the timing of caption text appearance as well as the probability of occurrence of attributes related to the shooting and editing techniques. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(6): 101–111, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1137
A replicated object relocation protocol for wide‐area networks
Authors: Watanabe Takashi , Mori Akifumi , Yamamoto Yukihisa
Published: August 2002

The distributed object directing technology has been attracting attention from the points of view of cost reduction and scalability. Such technology may not be easily accessible due to communication delays and changes when applied to wide‐area networks. For this problem, RORP (Replicated Object Relocation Protocol) by which a replicated object is dynamically relocated to an appropriate site, considering the communication delay between client and a server, site processing performance, frequency of referencing of the object, propagation time, and so on, is proposed. The RORP has the functions of sharing, reserving, renewing, and relocating a replicated object. First, each function of the RORP is explained. Next, a prototype using HORB and JAVA is constructed, and the performance of the RORP is evaluated from the points of view of the response time improvement effect, control messages, and the network occupation time of reference request and reply messages. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(7): 73–84, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1143
Hierarchical element decomposition of an articulated object based on its motion and shape and its application to measuring human body motion
Authors: Koara Kengo , Nishikawa Atsushi , Miyazaki Fumio
Published: August 2002

Decomposing an articulated object into its constituent elements is one of the basic techniques of image recognition and its applications to structural analyses or motion measurements of human and animal bodies are being studied. In this paper, a method of decomposing an object into elements based on its motion and shape while taking account of the distribution of high‐curvature points of the contour of the object is proposed for motion image sequences of objects, including objects considered to have two‐dimensionally moving, branchless, invariable link‐length elements and long multilink structures. Since the processing is based on the shape information obtained from all of the motion image sequences by this method, an object can be divided into regions in terms of the characteristic parts of the motion, even when the contour shape for each frame may be distorted by the effects of noise and the like, and therefore the method is very effective for preliminary processing or model building in measuring a body motion. In order to show the efficacy and an applicable example of the proposed method, the kip motion, which is a bar exercise, is measured. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(8): 98–110, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.1150
Atomic force microscopy of thin organic films on silicon in ultrahigh vacuum and under ambient conditions
Authors: Reiniger M. , Basnar B. , Friedbacher G. , Schleberger M.
Published: August 2002

In this paper we investigate thin organic films on silicon oxide by different atomic force microscopy (AFM) techniques. For the preparation of the organic films we chose octadecyltrichlorosilane (OTS), which shows a strong tendency for self‐assembly. As substrates we use silicon covered with a native silicon oxide. The self‐assembled monolayers are deposited in solution to give octadecylsiloxane (ODS) islands. Island density and size vary, among other things, with the solution age, its concentration and the deposition time. Growth and structure are investigated in air as well as in ultrahigh vacuum (UHV) with AFM. The measurements are performed in contact, non‐contact or tapping mode. We found that the ODS islands are 1.6 nm in height in UHV as well as under ambient conditions. From the length of the OTS molecules a height of 2.6 nm should be expected. We attribute the reduced height to a tilt of the alkyl chains. Damping maps show that the energy dissipation on the ODS islands is less than on the silicon oxide substrate. Copyright © 2002 John Wiley & Sons, Ltd.
ToF‐SIMS analysis of model compounds of friction modifier adsorbed onto friction surfaces of ferrous materials
Authors: Murase A. , Ohmori T.
Published: August 2002

The adsorption of model compounds of friction modifiers on ferrous materials has been investigated by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Eleven kinds of model compounds, including carboxylic acids, alcohols, amines and esters, were subjected to lubrication tests. Six compounds among these—carboxylic acids and some amines and esters—showed good lubricity. The ToF‐SIMS spectra of the friction surfaces after being washed with hexane showed that carboxylic acids formed Fe‐carboxylates by reacting with the ferrous material, and esters formed both Fe‐carboxylates and Fe‐alcoholates by reactions of hydrolysates of esters and the ferrous material. For amines, no reaction products were detected but quasimolecular ions, suggesting physical adsorption, were detected from the friction surfaces. For alcohols, no adsorption or reaction was detected from the friction surface. However, clear correlations were not found between the amounts of reaction products or adsorbed materials and lubrication properties such as friction coefficient and width of wear scar. Copyright © 2001 John Wiley & Sons, Ltd.
Characterization of a non‐organofunctional silane film deposited on Al, Zn and Al–43.4Zn–1.6Si alloy‐coated steel
Authors: Bexell Ulf , Olsson Mikael
Published: August 2002

The need to develop new environmentally friendly pretreatments in the surface engineering of metal substrates has become more and more important.This is mainly due to the toxic and carcinogenic properties of the chromium‐based surface pretreatments frequently used in the industry. During the last decade, simple solution‐dip silane‐based pretreatments have emerged as promising candidates for the replacement of currently used pretreatments of metals. Recent investigations have shown that the performance of these newly developed pretreatments is strongly dependent on the chemical composition and structure of the silane film and consequently a lot of work, based on advanced surface analytical techniques, is needed in order to characterize these properties. In the present study, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used to characterize the structure of thin films of the non‐organofunctional silane 1,2‐bis(triethoxysilyl)ethane (BTSE) deposited on three different metal substrates, i.e. Al, Zn and Al–43.4Zn–1.6Si (AlZn) alloy‐coated steel. Of special interest was an evaluation of the influence of substrate material on the structure and composition of the silane films.

The results show that the BTSE silane forms a thin, evenly distributed film over the substrate surfaces and that the molecular structure of the silane film is independent of the type of metal substrate. Analysis of the molecular ions in the positive mode shows that the surface structure of the BTSE silane is very complex and that the BTSE condensates via one to three SiOSi bridges. Also, the results show that the BTSE silane is not fully hydrolysed using a hydrolysing time of 1 h. Finally, if an alcohol is used as a solvent for the BTSE there is a clear chemical interaction between the alcohol and the silane, resulting in an exchange of alkoxy groups between the alcohol and the silane. Copyright © 2001 John Wiley & Sons, Ltd.
Estimating the efficacy of interventions to prevent mother‐to‐child transmission of HIV in breast‐feeding populations: development of a consensus methodology
Authors: Alioum Ahmadou , Dabis François , Dequae‐Merchadou Laurence , Haverkamp Geert , Hudgens Michael , Hughes James , Karon John , Leroy Valeriane , Newell Marie‐Louise , Richardson Barbra , Weverling Gerrit‐Jan
Published: August 2002

Postnatal transmission of HIV through breast milk complicates both the design of effective interventions to prevent mother‐to‐child transmission of HIV (PMTCT) and their evaluation. Estimated long‐term efficacy in five African trials (four with peri‐partum antiretrovirals and one with artificial feeding) varied from 25 to 50 per cent. This variation may be due, at least in part, to differences in analytical methodology. To facilitate direct comparison between trials, a methodological consensus approach to the analysis and presentation of the results of PMTCT trials was developed. The initial methodology used and results presented from African trials with available long‐term efficacy data were reviewed during a workshop in Bordeaux, France, in September 2000. A consensus approach for evaluating efficacy applicable across PMTCT studies was developed. There are four typical situations defined by duration of follow‐up (short versus long), and the available demographic (vital status) and biological data (single versus repeat HIV testing). Efficacy can be assessed from the risk of infection directly or from HIV‐free survival by combining infection and death as a single endpoint. Studies should report results in a standardized format including infection, weaning, mortality and loss to follow‐up. New statistical methods that account for the unknown date when a child would first test positive for HIV, for weaning as a competing risk for HIV infection, and for increased risk of death among HIV‐infected children should be used in analysing data from PMTCT studies with repeat HIV testing. All estimates should be reported with confidence intervals. This standardized methodology that allows direct comparison between studies is now being applied to four randomized clinical trials. Copyright © 2001 John Wiley & Sons, Ltd.
Prediction trees with soft nodes for binary outcomes
Authors: Ciampi Antonio , Couturier André , Li Shaolin
Published: August 2002

Consider the problem of predicting the occurrence of an event, the onset of diabetes mellitus, say, from a vector of continuous and discrete predictors. We propose a new algorithm for the construction of a tree‐structured predictor for the event of interest, which uses a new approach for dealing with continuous predictors. The novelty is that the tree uses splits for continuous variables. This means that at each node an individual goes to the right branch with a certain probability, function of a predictor. The predictor as well as the particular shape of the function is chosen from the data by the proposed algorithm. We evaluate its performance on several real data sets, in particular comparing it with a standard tree‐growing algorithm. We also present an analysis of a well‐known data set, the Pima Indian diabetes data set, to illustrate the application of the method in biostatistics. Copyright © 2002 John Wiley & Sons, Ltd.
Clinical trials of behavioural interventions with heterogeneous teaching subgroup effects
Authors: Hoover Donald R.
Published: August 2002

Behaviour modification is often delivered to teaching subgroups. For example, experimental and control smoking cessation programmes may be given to 15 classes (subgroups) with 10 (otherwise independent) individuals. We present general statistical tests and power estimates to compare continuous outcomes from two interventions in settings where the magnitude of teaching subgroup heterogeneity, number of subgroups and subgroup size can differ between intervention arms. An application is made to data from a trial to reduce disease‐transmitting sexual behaviour. The statistical impact of teaching subgroup heterogeneity effect increases as the (a) number of participants in a subgroup increases, and (b) ratio of ‘averaged experimental and control subgroup effect variance’ to study subject variance increases. If plausible levels of subgroup teaching effect heterogeneity are ignored, the true sizes of tests with nominal 0.05 two‐sided type I errors range from 0.055 to 0.47, while when planning studies, estimated sample sizes are only 11.1–95.2 per cent of the true requirements. Copyright © 2002 John Wiley & Sons, Ltd.
Data field standards and the Health Insurance Portability and Accountability Act
Authors: Braithwaite William R.
Published: August 2002

The Administrative Simplification Title of the Health Insurance Portability and Accountability Act of 1996 addresses the creation and adoption of nationwide standards for the electronic exchange and confidentiality protection of all individually identified data used in health care administration. The U.S. Department of Health and Human Services (DHHS) is implementing standards under this law. In addition to new standards, the law mandates that the Congress pass a health information privacy bill by August 1999 or that the DHHS adopt privacy protections for health information by February 2000. Published in 2001 by John Wiley & Sons, Ltd.
A dynamic adaptation of the propensity score adjustment for effectiveness analyses of ordinal doses of treatment
Authors: Leon Andrew C. , Mueller Timothy I. , Solomon David A. , Keller Martin B.
Published: August 2002

The propensity score adjustment is a method to reduce bias in observational studies. We propose a strategy that involves a novel combination of three data analytic techniques, which adapts the propensity adjustment for additional perturbations of longitudinal, observational studies. First, ordinal logistic regression examines propensity for ordinal doses of treatment. Second, a mixed‐model approach incorporates the multiple treatment trials and multiple episodes that are characteristic of chronically ill subjects. Finally, a mixed‐effects grouped‐time survival model incorporates the propensity score in treatment effectiveness analyses. The strategy that is applied here to an observational study of affective illness can also be used to evaluate the effectiveness of treatments for other chronic illnesses. Copyright © 2001 John Wiley & Sons, Ltd.
Assessing human fertility using several markers of ovulation
Authors: Dunson D. B. , Weinberg C. R. , Baird D. D. , Kesner J. S. , Wilcox A. J.
Published: August 2002

In modelling human fertility one ideally accounts for timing of intercourse relative to ovulation. Measurement error in identifying the day of ovulation can bias estimates of fecundability parameters and attenuate estimates of covariate effects. In the absence of a single perfect marker of ovulation, several error prone markers are sometimes obtained. In this paper we propose a semi‐parametric mixture model that uses multiple independent markers of ovulation to account for measurement error. The model assigns each method of assessing ovulation a distinct non‐parametric error distribution, and corrects bias in estimates of day‐specific fecundability. We use a Monte Carlo EM algorithm for joint estimation of (i) the error distribution for the markers, (ii) the error‐corrected fertility parameters, and (iii) the couple‐specific random effects. We apply the methods to data from a North Carolina fertility study to assess the magnitude of error in measures of ovulation based on urinary luteinizing hormone and metabolites of ovarian hormones, and estimate the corrected day‐specific probabilities of clinical pregnancy. Published in 2001 by John Wiley & Sons, Ltd.
Analysis of change in the presence of informative censoring: application to a longitudinal clinical trial of progressive renal disease
Authors: Schluchter Mark D. , Greene Tom , Beck Gerald J.
Published: August 2002

The rate of change in a continuous variable, measured serially over time, is often used as an outcome in longitudinal studies or clinical trials. When patients terminate the study before the scheduled end of the study, there is a potential for bias in estimation of rate of change using standard methods which ignore the missing data mechanism. These methods include the use of unweighted generalized estimating equations methods and likelihood‐based methods assuming an ignorable missing data mechanism. We present a model for analysis of informatively censored data, based on an extension of the two‐stage linear random effects model, where each subject's random intercept and slope are allowed to be associated with an underlying time to event. The joint distribution of the continuous responses and the time‐to‐event variable are then estimated via maximum likelihood using the EM algorithm, and using the bootstrap to calculate standard errors. We illustrate this methodology and compare it to simpler approaches and usual maximum likelihood using data from a multi‐centre study of the effects of diet and blood pressure control on progression of renal disease, the Modification of Diet in Renal Disease (MDRD) Study. Sensitivity analyses and simulations are used to evaluate the performance of this methodology in the context of the MDRD data, under various scenarios where the drop‐out mechanism is ignorable as well as non‐ignorable. Copyright © 2001 John Wiley & Sons, Ltd.
Revision of the ICIDH Severity of Disabilities Scale by data linking and item response theory
Authors: van Buuren S. , Hopman‐Rock M.
Published: August 2002

The Severity of Disabilities Scale (SDS) of the ICIDH reflects the degree to which an individual's ability to perform a certain activity is restricted. This paper describes the application of two models from item response theory (IRT), the graded response model and the partial credit model, in order to derive a tentative proposal for a revised SDS. The key ingredient of the approach is to scale existing disability items obtained in different studies on a common scale by exploiting the overlap. Both IRT models are fitted to a linked data set containing items for measuring walking disability. Based on these solutions, a tentative SDS is constructed. The paper concludes with a discussion of the implications, limitations and advantages of the approach. Copyright © 2001 John Wiley & Sons, Ltd.
Logistic discrimination of mixtures of M. tuberculosis and non‐specific tuberculin reactions
Authors: Nagelkerke Nico J. D. , Borgdorff Martien W. , Kim Sang Jae
Published: August 2002

Interpretation of the Mantoux test for tuberculous infection can be complicated by cross‐reactions caused by infection with non‐specific mycobacteria. Thus, the distribution of positive indurations is a mixture of two distributions. To estimate tuberculous infection prevalence, the marginal distribution of indurations needs to be separated into its component distributions. Observations from several populations with different mixes of the two types of infection are required. Homogeneity across populations of distributions of indurations for each type of infection is assumed. A logistic model is specified for the probability of having tuberculous infection conditional on the observed induration size. No other assumptions about the two distributions are made. Maximum likelihood is used to estimate the logistic function. Goodness‐of‐fit criteria are discussed. The method is applied to a series of tuberculin surveys carried out in (South) Korea. Estimated infection prevalence agrees reasonably well with severalad hoccriteria. The goodness‐of‐fit test rejects underlying assumptions of homogeneity. One reason appears to be a decline over time in induration sizes caused by tuberculous infection. However, not all reasons for this rejection are obvious. The proposed method of mixture analysis provides an additional tool for the interpretation of prevalence survey data where the diagnostic test lacks specificity as a result of cross‐reactions. Copyright © 2001 John Wiley & Sons, Ltd.
Important ECG diagnosis‐aiding indices of ventricular septal defect children with or without congestive heart failure
Authors: Guo Meihui , Huang Mong‐Na Lo , Bai Zhidong , Hsieh Kai‐Sheng
Published: August 2002

In this paper we perform a statistical study of the conventional RR intervals and two newly defined PR′ and RT intervals of ECG data. A quadratic classification rule is applied to extract several important ECG diagnosis‐aiding indices among normal children and children with ventricular septal defect (VSD) with or without congestive heart failure (CHF). The results show that certain statistics computed from PR′, RR and RT intervals are important diagnosis‐aiding indices. Best classification vectors are searched for pairwise classification. Two methods, minimum distance criterion and a two‐stage classification procedure, are considered for three‐way classification. Furthermore, logistic regression models based on transformations of these important diagnosis‐aiding indices are proposed. The receiver operating characteristic curves of the proposed models show better performance than those of linear and quadratic logistic models. In order to proceed with this study, a computer algorithm to automatically detect the three intervals is developed and the related ECG data are collected and analysed. The algorithm is also enhanced with an outlier detection procedure for the automatic measurements of the PR′ and RT intervals. Copyright © 2001 John Wiley & Sons, Ltd.
Modification of pharmacokinetic sampling schedules in clinical phase I trials: a use of Kullback–Leibler information
Authors: Yafune Akifumi , Ishiguro Makio
Published: August 2002

In clinical phase I trials, pharmacokinetic sampling schedules often have to be modified while the trials proceed. The modifications are based on the observations from a limited number of subjects or only one subject in extreme cases. This paper describes a Kullback–Leibler information approach for modifying pharmacokinetic sampling schedules in clinical phase I trials. The proposed approach presupposes that the pharmacokinetic profile for each subject is specified by an appropriate pharmacokinetic model and the subject‐specific parameters. The best modification plan is selected from arbitrarily chosen candidates based on the Kullback–Leibler information. Applications are given to a simulation study and an actual phase I trial of an anti‐cancer drug. Copyright © 2001 John Wiley & Sons, Ltd.
Joint testing of mortality and a non‐fatal outcome in clinical trials
Authors: McMahon Robert P. , Harrell Frank E.
Published: August 2002

The following procedures are proposed for clinical trials of potentially lethal diseases with a non‐fatal primary outcome: (i) comparison of treatments on worst‐rank scores combining mortality and the non‐fatal outcome; (ii) testing first for mortality differences, and then for differences on the worst‐rank scoring if there is no significant evidence for mortality differences. Power and control of type I error rate while testing mortality and worst‐rank scores by Bonferroni or closed testing procedures are compared. Used together these procedures improve power to detect treatments with favourable effects on both mortality and the designated non‐fatal outcome, while reducing the likelihood of declaring that a treatment benefits patients when undetected adverse effects on mortality are present. Copyright © 2001 John Wiley & Sons, Ltd.
Event history graphs for censored survival data
Authors: Dubin Joel A. , Müller Hans‐Georg , Wang Jane‐Ling
Published: August 2002

A compact graphical device for combining survival and time‐varying covariate information is proposed. The proposed graph contains the Kaplan–Meier estimator for right‐censored data and a simultaneous display of the behaviour of time‐dependent covariate(s) and the lifetime for each subject in the sample. The observed levels of time‐dependent covariates are possibly subjected to an initial dimension reduction or smoothing step to produce a continuous covariate function. Values of this function are plotted on a horizontal bar for the length of the lifetime of the subject. Covariate information for censored data is also incorporated. The union of the horizontal bars forms the Kaplan–Meier estimator of the survival function. Our graphical method is implemented with a new S‐plus function and demonstrated in several applications. Copyright © 2001 John Wiley & Sons, Ltd.
Estimation of non‐parametric multivariate risk functions in matched case‐control studies with application to the assessment of interactions of risk factors in the study of cancer
Authors: van der Linde Angelika , Osius Gerhard
Published: August 2002

In epidemiological studies one is interested in investigating the probability of disease depending on risk factors and in particular in detecting interactions of risk factors. Within the setting of parametric logistic regression, interactions can be modelled only in a clumsy and limited way. Modelling the risk function non‐parametrically, estimating it, for example, by a smoothing (thin plate) spline is attractive as a more explorative approach. For prospective studies this amounts to smoothing within the framework and distributional assumptions of generalized regression models (for binary observations). Case‐control studies as retrospective studies with exposure to risk factors being observed do not immediately fit into this setting. In the special case of one‐to‐one matched studies, however, there is an appropriate likelihood again within the range of generalized models. Inferences will be illustrated using simulated and real data. Copyright © 2001 John Wiley & Sons, Ltd.
A scheme for a dose‐escalation study when the event is lagged
Authors: Hüsing Johannes , Sauerwein Wolfgang , Hideghéty Katalin , Jöckel Karl‐Heinz
Published: August 2002

Classical designs for clinical phase I trials assume that information about a dose‐limiting event (DLE) is available for all the included patients, or advise not to treat new patients until the information is present. If a DLE occurs after a lag, however, information at the current time might not be sufficient to make clear‐cut decisions according to these designs. In particular, if new patients are available, it is not clear whether to include them in the trial. We suggest a rule that decides on the accrual of each individual eligible patient. Simulation studies are presented that indicate an advantage over the standard ‘three‐at‐once’ design in the length of the study. Copyright © 2001 John Wiley & Sons, Ltd.
A local likelihood proportional hazards model for interval censored data
Authors: Betensky Rebecca A. , Lindsey Jane C. , Ryan Louise M. , Wand M. P.
Published: August 2002

We discuss the use of local likelihood methods to fit proportional hazards regression models to right and interval censored data. The assumed model allows for an arbitrary, smoothed baseline hazard on which a vector of covariates operates in a proportional manner, and thus produces an interpretable baseline hazard function along with estimates of global covariate effects. For estimation, we extend the modified EM algorithm suggested by Betensky, Lindsey, Ryan and Wand. We illustrate the method with data on times to deterioration of breast cosmeses and HIV‐1 infection rates among haemophiliacs. Copyright © 2002 John Wiley & Sons, Ltd.
Reproducibility of cardiovascular responses to mental and static tasks
Authors: Seibt Reingard , Scheuch Klaus , Hinz Andreas
Published: August 2002

Temporal stability and transsituational consistency are important characteristics of cardiovascular responses to mental or static load. While in the literature stability is generally estimated as the relationship between only two test sessions, it is unknown whether these stability estimates can be generalized across multiple replications of the test situations. Forty subjects (20 males and 20 females) were tested four times with intervals of 1 day, 1 week, and 1 month. Each test session comprised two mental tasks (mental arithmetic and colour–word test) and a static (fingergrip) task. The physiological variables recorded were heart rate, systolic blood pressure, and diastolic blood pressure. The adaptation processes in the course of the four test sessions are more pronounced for the mental tests than for the static test. The temporal stability, restricted to test sessions 1 and 2, can be used to estimate the general stability across all pairs of test sessions. However, there are some non‐systematic differences which indicate that more than two test sessions yield more reliable results. Averaging across two test sessions, compared with the stability of single test sessions, increases the stability of heart rate reactivity from 0.60 to 0.73. Low correlations between the responses to mental and static load indicate that there are different underlying regulatory mechanisms. The results show that the responsivity can be assessed more reliably when more than two tests are performed. The responses to one type of stressors (mental or static) cannot be generalized to an overall responsivity. Copyright © 2001 John Wiley & Sons, Ltd.
Effect of public speaking on gastric myoelectrical reactivity and parasympathetic cardiac control
Authors: Codispoti Maurizio , Mazzetti Michela , Baldaro Bruno , Tuozzi Giovanni , Trombini Giancarlo
Published: August 2002

Gastrointestinal reactivity is a central concept in several psychosomatic approaches to peptic ulcer disease and irritable bowel disease. One potential limitation of many laboratory studies of gastrointestinal reactivity is their reliance on non‐ecological tasks lacking components of social stressors which may better relate to day to day stress. Otherwise, the public speaking task is a well known stressful procedure and has a high degree of ecological validity. Stress reactions induced by preparation for public speaking are the result of both the cognitive demand of preparing a speech and social anxiety. The aim of this study was to observe the effect of the public speaking test on the electrogastric activity and the relationship between gastric myoelectrical activity and cardiac activity prior to and after the task. In particular, we hypothesized that public speaking would reduce the amplitude of the normal 3 c.p.m. band and that this decrease would be positively correlated with a reduction in respiratory sinus arrhythmia. As expected, the anticipation of public speaking triggered a decrease in respiratory sinus arrhythmia, an increase in heart rate, and higher skin conductance level compared to baseline. On the other hand, our measure of gastric myoelectrical activity was not affected by the public speaking task. Copyright © 2001 John Wiley & Sons, Ltd.
Self‐esteem, personality and post traumatic stress symptoms following the dissolution of a dating relationship
Authors: Chung Man Cheung , Farmer Steven , Grant Keren , Newton Rebecca , Payne Sally , Perry Melissa , Saunders Jenny , Smith Charlotte , Stone Nina
Published: August 2002

The present study aimed to ascertain the extent to which people, following the dissolution of a dating relationship, experienced post traumatic stress symptoms. It also aimed to investigate the relationship between post traumatic stress and self‐esteem and personality. The hypotheses were that there would be a severe degree of post traumatic stress symptoms experienced by the present samples, and that the personality factor, in particular, neuroticism, and low self‐esteem would be associated with the samples' post traumatic stress symptoms. Sixty heterosexual subjects who had experienced a romantic relationship dissolution over the past 24 months were recruited for the study. They were interviewed with the Impact of Event Scale (IES), the General Health Questionnaire‐28 (GHQ‐28), the Self‐Esteem Rating Scale (SERS) and the Eysenck Personality Questionnaire‐R Short Scale (EPQ‐R). The results showed that 72 per cent of the subjects scored at or above the high IES symptom cut‐off. Forty‐three per cent scored above the cut‐off of the GHQ‐28. Significant correlations were found between the impact of the dissolution and general health. The present subjects were significantly less extroverted and neurotic than the standardized samples. Stepwise regression analyses showed that negative self‐esteem significantly predicted avoidance and the total general health, and that neuroticism significantly predicted the total impact of the dissolution. Copyright © 2002 John Wiley & Sons, Ltd.