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D Y Lin

Publications and source records attributed to D Y Lin.

At least 37 records · Page 2Linked to original sources
PubMed2003

Regression analysis of incomplete medical cost data.

The accumulation of medical cost over time for each subject is an increasing stochastic process defined up to the instant of death. The stochastic structure of this process is complex. In most applications, the process can only be observed at a limited number of time points. Furthermore, the process is subject to right censoring so that it is unobservable after the censoring time. These special features of the medical cost data, especially the presence of death and censoring, pose major challenges in the construction of plausible statistical models and the development of the corresponding inference procedures. In this paper, we propose several classes of regression models which formulate the effects of possibly time-dependent covariates on the marginal mean of cost accumulation in the presence of death or on the conditional means of cost accumulation given specific survival patterns. We then develop estimating equations for these models by combining the approach of generalized estimating equations for longitudinal data with the inverse probability of censoring weighting technique. The resultant estimators are shown to be consistent and asymptotically normal with simple variance estimators. Simulation studies indicate that the proposed inference procedures behave well in practical situations. An application to data taken from a large cancer study reveals that the Medicare enrollees who are diagnosed with less aggressive ovarian cancer tend to accumulate medical cost at lower rates than those with more aggressive disease, but tend to have higher lifetime costs because they live longer.

Aged↗
PubMed2003

Incremental net benefit in randomized clinical trials with quality-adjusted survival.

Owing to induced dependent censoring, estimating mean costs and quality-adjusted survival in a cost-effectiveness comparison of two groups using standard life-table methods leads to biased results. In this paper we propose methods for estimating the difference in mean costs and the difference in mean effectiveness, together with their respective variances and covariance in the presence of dependent censoring. We consider the situation in which the measure of effectiveness is either the probability of surviving a duration of interest or mean quality-adjusted survival time over a duration of interest. The methods are illustrated in an example using an incremental net benefit analysis.

Amiodarone↗
PubMed2003

Semiparametric regression analysis of longitudinal data with informative drop-outs.

Informative drop-out arises in longitudinal studies when the subject's follow-up time depends on the unobserved values of the response variable. We specify a semiparametric linear regression model for the repeatedly measured response variable and an accelerated failure time model for the time to informative drop-out. The error terms from the two models are assumed to have a common, but completely arbitrary joint distribution. Using a rank-based estimator for the accelerated failure time model and an artificial censoring device, we construct an asymptotically unbiased estimating function for the linear regression model. The resultant estimator is shown to be consistent and asymptotically normal. A resampling scheme is developed to estimate the limiting covariance matrix. Extensive simulation studies demonstrate that the proposed methods are suitable for practical use. Illustrations with data taken from two AIDS clinical trials are provided.

Child↗
PubMed2003

Semiparametric analysis of recurrent events data in the presence of dependent censoring.

Dependent censoring occurs in longitudinal studies of recurrent events when the censoring time depends on the potentially unobserved recurrent event times. To perform regression analysis in this setting, we propose a semiparametric joint model that formulates the marginal distributions of the recurrent event process and dependent censoring time through scale-change models, while leaving the distributional form and dependence structure unspecified. We derive consistent and asymptotically normal estimators for the regression parameters. We also develop graphical and numerical methods for assessing the adequacy of the proposed model. The finite-sample behavior of the new inference procedures is evaluated through simulation studies. An application to recurrent hospitalization data taken from a study of intravenous drug users is provided.

Biometry↗
PubMed2002

Model-checking techniques based on cumulative residuals.

Residuals have long been used for graphical and numerical examinations of the adequacy of regression models. Conventional residual analysis based on the plots of raw residuals or their smoothed curves is highly subjective, whereas most numerical goodness-of-fit tests provide little information about the nature of model misspecification. In this paper, we develop objective and informative model-checking techniques by taking the cumulative sums of residuals over certain coordinates (e.g., covariates or fitted values) or by considering some related aggregates of residuals, such as moving sums and moving averages. For a variety of statistical models and data structures, including generalized linear models with independent or dependent observations, the distributions of these stochastic processes tinder the assumed model can be approximated by the distributions of certain zero-mean Gaussian processes whose realizations can be easily generated by computer simulation. Each observed process can then be compared, both graphically and numerically, with a number of realizations from the Gaussian process. Such comparisons enable one to assess objectively whether a trend seen in a residual plot reflects model misspecification or natural variation. The proposed techniques are particularly useful in checking the functional form of a covariate and the link function. Illustrations with several medical studies are provided.

Adolescent↗
PubMed2002

Using inverse-weighting in cost-effectiveness analysis with censored data.

Due to induced dependent censoring, estimating mean costs and quality-adjusted survival in a cost-effectiveness analysis using standard life-table methods leads to biased results. In this paper we propose methods for estimating the difference in mean costs and the difference in effectiveness, together with their respective variances and covariance in the presence of dependent censoring. We consider the situation in which the measure of effectiveness is either the probability of patients surviving a duration of interest, mean survival time over a duration of interest or mean quality-adjusted survival time over a duration of interest. The method of inverse-weighting is used for censored cost and quality of life data. The methods are illustrated in an example using an incremental net benefit analysis.

Cost-Benefit Analysis↗
PubMed2001

Incremental net benefit in randomized clinical trials.

There are three approaches to health economic evaluation for comparing two therapies. These are (i) cost minimization, in which one assumes or observes no difference in effectiveness, (ii) incremental cost-effectiveness, and (iii) incremental net benefit. The latter can be expressed either in units of effectiveness or costs. When analysing data from a clinical trial, expressing incremental net benefit in units of cost allows the investigator to examine all three approaches in a single graph, complete with the corresponding statistical inferences. Furthermore, if costs and effectiveness are not censored, this can be achieved using common two-sample statistical procedures. The above will be illustrated using two examples, one with censoring and one without.

Amiodarone↗
PubMed2001

Epidemiological characteristics, risk factors, and clinical manifestations of acute non-A-E hepatitis.

A substantial proportion of acute non-A, non-B hepatitis was of unknown etiology and was termed non-A-E hepatitis. Analysis of the clinical features is needed while attempting to identify the causative agent(s). In this study, the clinical and biochemical features of 53 patients who were admitted to hospital with acute non-A-E hepatitis were compared with a cohort of patients with acute hepatitis C (n = 70) and E (n = 5). In acute non-A-E hepatitis, the sex ratio was 34:19, and ages ranged from 21 to 76 years (median 49). Biochemical tests [median (range)] revealed albumin 3.6 (2.2-4.4) g/dl, AST 714 (193-2311) U/l, ALT 896 (310-3,000) U/l, bilirubin 11.2 (0.9-36.3) mg/dl, and prothrombin time > 1.1 (0-11.5) seconds. No patients reported parenteral exposures or household contact. Forty-five percent had severe hepatitis (i.e., albumin < 3 g/dl, bilirubin > 15 mg/dl or prothrombin time > 3 sec), including 3% with fulminant hepatitis. Chronic evolution was noted in 7%. These features were similar to those of hepatitis C or E, except for a significantly high frequency of parenteral exposures (20%), household contact (16%), and chronicity (70%) in hepatitis C. In conclusion, there is no obvious parenteral risk factor identified in acute non-A-E hepatitis. Clinical severity is similar to that of hepatitis C at least in hospitalized patients, but the rate of chronic evolution is much lower.

Acute Disease↗
PubMed2001

Nonparametric tests for the gap time distributions of serial events based on censored data.

This article deals with the problem of comparing two populations with respect to the distribution of the gap time between two successive events when each subject can experience a series of events and when the event times are potentially right censored. Several families of nonparametric tests are developed, all of which allow arbitrary distributions and dependence structures for the serial events. The asymptotic and small-sample properties of the proposed tests are investigated. An illustration with data taken from a colon cancer study is provided. The related problem of testing the independence of two successive gap times is also studied.

Chemotherapy, Adjuvant↗
PubMed2001

Correlation of mutational analysis to clinical features in Taiwanese patients with Gilbert's syndrome.

OBJECTIVES: Mutations in the promoter as well as in the coding region of the bilirubin UDP-glucuronosyltransferase gene (UGT1A1) have been found to be associated with Gilbert's syndrome. However, the genetic basis of Gilbert's syndrome in our population and correlation of these mutations to fasting serum bilirubin levels in patients with Gilbert's syndrome remain to be clarified. METHODS: We applied polymerase chain reaction-based direct-sequencing assays to examine mutations in UGT1A1 gene in 20 unrelated Gilbert's patients and in a family with Gilbert's syndrome. RESULTS: We studied three mutations that were previously reported to be associated with Gilbert's syndrome (i.e., the TATAA-box mutation, Gly71Arg, and Pro229Gln) in 20 patients with Gilbert's syndrome. Of the patients, 16, five, and six were found to have the TATAA-box, Gly71Arg and Pro229Gln mutations, respectively. Seven patients had simultaneous mutations both in the TATAA box and in the coding region. Of note, all six patients with Pro229Gln also had the TATAA-box mutation. Localization of Pro229Gln on the allele containing the TATAA-box mutation was demonstrated in a family with Gilbert's syndrome. The patients simultaneously heterozygous for both the TATAA-box mutation and Gly71Arg usually had serum bilirubin levels similar to those found in the patients homozygous for the TATAA-box mutation, but usually higher than those found in the patients heterozygous for the TATAA-box mutation alone. On the other hand, concurrence of Pro229Gln in patients with TATAA-box mutation or with Gly71Arg did not significantly affect serum bilirubin levels. CONCLUSIONS: The TATAA-box mutation and Gly71Arg are the major causes for Gilbert's syndrome in our population. Concurrence of mutations of Gly71Arg and TATAA-box usually exerts a synergistic effect on hyperbilirubinemia. Pro229Gln, which is regularly linked to the TATAA-box mutation, may not have a significant effect on serum bilirubin levels.

Adolescent↗
PubMed2001

Acute jejunogastric intussusception: report of five cases.

The purpose of this study was to investigate the clinical manifestations and diagnosis of patients with acute jejunogastric intussusception. From May 1986 to June 1999, a total of 5 men (54-76 years old) were collected. Their initial presentations included epigastralgia (4), coffee-ground vomitus (3), frank hematemesis (1), and tarry stool (1). All patients had gastric surgeries 10-30 years previously. Radiograph of the abdomen showed a soft tissue density at the left upper quadrant in one patient. Panendoscopies were done in 4 patients. An obstructed efferent loop with a distended hyperemic small bowel protruding into the remnant of stomach was found in 3 cases, gangrenous change of the bowel wall in one of them. Stump cancer was diagnosed initially in the other patient. Barium study (3/5) showed efferent loop obstruction with "coil spring sing" and a central defect in the stomach. All 5 patients underwent segmental resection and end-to-end anastomosis between the 2nd to 6th hospital day. Operative findings were type II jejunogastric intussusception with retrograde invagination of a segment of efferent loop (30-100 cm in length) into the stomach. In conclusion, acute jejunogastric intussusception is an emergent condition. Early and accurate diagnosis is important. A high susception must be kept in mind in patients having a history of gastrojejunostomy with severe abdominal pain or upper gastrointestinal bleeding.

Acute Disease↗
PubMed2000

The study of TSP, PM(2.5-10) and PM2.5 during Taiwan Chi-Chi Earthquake in the traffic site of central Taiwan, Taichung.

Ambient particle concentration was taken on the traffic sampling site over the Chung-Chi Road over bridge (CCROB) in front of Hungkuang Institute of Technology (HKIT). The sampling time was from August 1999 to December 1999. During the sampling period, Taiwan's biggest earthquake in more than a century registered 7.3 on the Richter scale (Taiwan Chi-Chi Earthquake). Besides, there were more than 20,000 aftershocks that followed the Taiwan Chi-Chi Earthquake within three months. Thus, the PM2.5, PM(2.5-10) particle concentrations were also collected then and compared with total suspended particle (TSP) in this study. The average PM(2.5-10), PM2.5 and TSP concentrations are 24.6, 58.0 and 106 microg/m3, respectively, after the Taiwan Chi-Chi Earthquake. The average TSP concentrations before and after Taiwan Chi-Chi Earthquake were 70 and 127 microg/m3, respectively. It is clearly shown that the average concentration of TSP after Taiwan Chi-Chi Earthquake was about 1.8 times as that of TSP concentration before Taiwan Chi-Chi Earthquake in the traffic site of central Taiwan. And the ratios of PM2.5/PM(2.5-10), PM2.5/PM10 and PM2.5/TSP are 2.2%, 67.2%, 38.9%, respectively. The results also indicated about Chi-Chi fine particle concentration (PM25) and the TSP increases in the traffic site of central Taiwan after Taiwan Chi-Chi Earthquake.

Air Pollutants↗
PubMed2000

Linear regression analysis of censored medical costs.

This paper deals with the problem of linear regression for medical cost data when some study subjects are not followed for the full duration of interest so that their total costs are unknown. Standard survival analysis techniques are ill-suited to this type of censoring. The familiar normal equations for the least-squares estimation are modified in several ways to properly account for the incompleteness of the data. The resulting estimators are shown to be consistent and asymptotically normal with easily estimated variance-covariance matrices. The proposed methodology can be used when the cost database contains only the total costs for those with complete follow-up. More efficient estimators are available when the cost data are recorded in multiple time intervals. A study on the medical cost for ovarian cancer is presented.

Journal Article↗
PubMed2000

Nonparametric analysis of recurrent events and death.

This article is concerned with the analysis of recurrent events in the presence of a terminal event such as death. We consider the mean frequency function, defined as the marginal mean of the cumulative number of recurrent events over time. A simple nonparametric estimator for this quantity is presented. It is shown that the estimator, properly normalized, converges weakly to a zero-mean Gaussian process with an easily estimable covariance function. Nonparametric statistics for comparing two mean frequency functions and for combining data on recurrent events and death are also developed. The asymptotic null distributions of these statistics, together with consistent variance estimators, are derived. The small-sample properties of the proposed estimators and test statistics are examined through simulation studies. An application to a cancer clinical trial is provided.

Antineoplastic Agents, Alkylating↗
PubMed2000

Proportional means regression for censored medical costs.

The semiparametric proportional means model specifies that the mean function for the cumulative medical cost over time conditional on a set of covariates is equal to an arbitrary baseline mean function multiplied by an exponential regression function. We demonstrate how to estimate the vector-valued regression parameter using possibly censored lifetime costs. The estimator is consistent and asymptotically normal with an easily estimable covariance matrix. Simulation studies show that the proposed methodology is appropriate for practical use. An application to AIDS is provided.

AIDS-Related Opportunistic Infections↗
PubMed2000

Survival analysis in clinical trials: past developments and future directions.

The field of survival analysis emerged in the 20th century and experienced tremendous growth during the latter half of the century. The developments in this field that have had the most profound impact on clinical trials are the Kaplan-Meier (1958, Journal of the American Statistical Association 53, 457-481) method for estimating the survival function, the log-rank statistic (Mantel, 1966, Cancer Chemotherapy Report 50, 163-170) for comparing two survival distributions, and the Cox (1972, Journal of the Royal Statistical Society, Series B 34, 187-220) proportional hazards model for quantifying the effects of covariates on the survival time. The counting-process martingale theory pioneered by Aalen (1975, Statistical inference for a family of counting processes, Ph.D. dissertation, University of California, Berkeley) provides a unified framework for studying the small- and large-sample properties of survival analysis statistics. Significant progress has been achieved and further developments are expected in many other areas, including the accelerated failure time model, multivariate failure time data, interval-censored data, dependent censoring, dynamic treatment regimes and causal inference, joint modeling of failure time and longitudinal data, and Baysian methods.

Biometry↗