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B C Choi

Publications and source records attributed to B C Choi.

At least 19 recordsLinked to original sources
PubMed1999

Classification of the first web space free flap of the foot and its applications in reconstruction of the hand.

Owing to its unique anatomic arterial supply and dual nerve innervation, the first web space of the foot can be used to harvest various sizes and shapes of flaps, which the authors have classified into four types according to their usage in hand reconstruction. This in turn depends on the site, shape, and size of the soft-tissue defect in the hand. Web skin flaps (n = 8) were used in prevention of contracture in the first web space and for proximal finger reconstruction. Two-island skin flaps (n = 4) were used to resurface the pulp defect in two adjacent fingers. In severe adduction contracture of the first web space, fill-up web flaps (n = 10) were used to replace the volume defect after a release procedure in the hand. Adjuvant web flaps (n = 9) were used in wrap-around procedures, in dorsalis pedis flap transfer, and in vascularized joint transfer to supplement the main flaps and to restore sensation in the reconstructed area. In the past 10 years up to February of 1998, a total of 31 patients with soft-tissue defects in the hand and fingers were reconstructed using the web space free flap with flap survival rate of 100 percent. The mean static 2-point discrimination was 8.5 (7.2 to 10) mm, and the mean first web angle was 86 degrees. The advantage of the first web space flap from the foot is that it can easily be harvested to match various sizes and shapes of defects in the hand and fingers. In addition, because of the anatomic similarity in contour, thickness, texture, and nerve innervation with the hand, the sensory restoration is excellent with minimal morbidity at the donor site. By classifying the flaps into four types according to various sizes, shapes, and the site from which the flap are harvested, clinical usefulness in various types of hand and finger reconstruction was confirmed.

Adolescent↗
PubMed1999

Comparison of methods of point estimation in occupational epidemiologic studies.

Two common study designs of occupational epidemiologic studies are cohort mortality studies, which use the population at risk as a denominator, and proportionate mortality studies, which use the total number of events as a denominator. This study compared the various methods of point estimation for cohort mortality studies, i.e., RR (risk ratio), OR (odds ratio) and SMR (standardized mortality ratio), and those for proportionate mortality studies, i.e., PRR (proportionate risk ratio), POR (proportionate odds ratio) and PMR (proportionate mortality ratio). This study was based on a real dataset of all workers in Metropolitan Toronto, Canada, who applied for compensation for various types of injuries or diseases from the Workers' Compensation Board in 1980. Results showed that within the cohort mortality or proportionate mortality study designs, OR (or POR) in all cases gave the least conservative estimates (farthest away from the null value), while SMR (or PMR) gave the most conservative estimates. The empirical differences between the point estimators were generally small. Our results showed that between study designs the corresponding point estimators were poorly correlated. In addition, this empirical study indicated that the use of the mortality odds ratio did not improve the proportionate mortality study very much in terms of generating results similar to the risk ratio from the cohort mortality design. We drew two conclusions: first, the point estimators within each study design can generally be a good alternative to one another; and second, proportionate mortality studies are not a good approximation for cohort mortality studies.

Cohort Studies↗
PubMed1998

Slopes of a receiver operating characteristic curve and likelihood ratios for a diagnostic test.

This paper clarifies two important concepts in clinical epidemiology: the slope of a receiver operating characteristic (ROC) curve and the likelihood ratio. It points out that there are three types of slopes in an ROC curve--the tangent at a point on the curve, the slope between the origin and a point on the curve, and the slope between two points on the curve. It also points out that there are three types of likelihood ratios that can be defined for a diagnostic test that produces results on a continuous scale--the likelihood ratio for a particular single test value, the likelihood ratio for a positive test result, and the likelihood ratio for a test result in a particular level or category. It further illustrates mathematically and empirically the following three relations between these various definitions of slopes and likelihood ratios: 1) the tangent at a point on the ROC curve corresponds to the likelihood ratio for a single test value represented by that point; 2) the slope between the origin and a point on the curve corresponds to the positive likelihood ratio using the point as a criterion for positivity; and 3) the slope between two points on the curve corresponds to the likelihood ratio for a test result in a defined level bounded by the two points. The likelihood ratio for a single test value is considered an important parameter for evaluating diagnostic tests, but it is not easily estimable directly from laboratory data because of limited sample size. However, by using ROC analysis, the likelihood ratio for a single test value can be easily measured from the tangent. It is suggested that existing ROC analysis software be revised to provide estimates for tangents at various points on the ROC curve.

Creatine Kinase↗
PubMed1998

Reducing variability in treatment decision-making: effectiveness of educating clinicians about uncertainty.

The objective of this study was to investigate whether or not education about the concept of uncertainty reduced variability in treatment decision-making. Three small groups of dentists in North York, Canada were asked to make restorative treatment decisions about simulated bitewing radiographs. They subsequently took part in a seminar about variations in perception and judgement and were given explanations of sensitivity, specificity and receiver operating characteristic (ROC) curve analysis. A repeat reading of the radiographs was then performed by both test and control groups. Results indicated that the intervention increased the accuracy, and decreased the variability of dentists' restorative treatment decisions. Kappa statistics were 0.33, 0.34 and 0.31 before the seminar, and 0.40, 0.43 and 0.41 after the seminar. Standard errors for kappas were 0.06, 0.05 and 0.05 before the seminar, and 0.02, 0.02 and 0.05 after the seminar. The area under the ROC curve was 0.7136 before the seminar and 0.7835 after the seminar. The data demonstrate that the dentists' decisions were less variable and more accurate following the educative intervention. This study suggests that there is potential for improving consistency and accuracy in clinical decision-making through education in probabilistic reasoning.

Adult↗
PubMed1998

Perspectives on epidemiologic surveillance in the 21st century.

This paper describes the importance of epidemiologic surveillance as a systematic, ongoing and population-based system for early warning and program development in the 21st century. Such a system routinely collects data on three classes of indicators (health outcomes, risk factors and intervention strategies) to set up both an early warning system (to identify associations and make predictions on health outcomes) and a program development system (to assess the need for intervention strategies, to plan and implement such strategies and to assess their effectiveness). A comprehensive surveillance system must be systematic (evidence-based selection of indicators, not hypothesis-driven), ongoing (continuous data collection, including repeated surveys) and population-based (whole population, or representative samples of the population). Such a system need not be developed from scratch, but can be based on linkage of existing databases and collection of additional information for identified data gaps. The initial steps for selecting indicators and creating a prototype framework for a comprehensive surveillance system are proposed to stimulate further discussion. It is suggested that surveillance systems should be more widely used in public health.

Community Health Planning↗
PubMed1997

Causal modeling to estimate sensitivity and specificity of a test when prevalence changes.

The objective of this paper is to demonstrate, by causal modeling, whether the sensitivity and specificity of a test are constant, or whether they change with prevalence. I use three assumptions, diagnostic, predictive, and correlational, in three sets of mathematical models. A diagnostic test measures an outcome of a disease and is based on the assumption that the "gold standard" result indicates a disease state that causes a test result. A predictive test measures a risk factor for a disease and is based on the assumption that the test result indicates a risk factor that causes a disease state. A correlational test measures a condition which is an outcome of an underlying causal risk factor for a disease and is based on the assumption that the disease and the test result are noncausally related. I find that sensitivity and specificity are constant for diagnostic tests but change with prevalence for predictive and correlational tests. I present equations to show the effects on various test performance indices when prevalence changes. Different equations must be used to estimate the sensitivity, specificity, and other test performance indicators for various types of tests that are under different causal assumptions.

Diagnostic Tests, Routine↗
PubMed1997

Estimating the economic costs of the abuse of tobacco, alcohol and illicit drugs: a review of methodologies and Canadian data sources.

The study of economic costs of substance abuse, namely, abuse of tobacco, alcohol and illicit drugs, can provide important information for setting good public health policies. This review paper provides a list of previous cost studies of substance abuse, compares the cost categories considered by various methodologies and describes an inventory of data sources for obtaining relevant information for cost studies. Investigators will find this paper useful as an introduction to the literature in this area, for designing a list of cost categories to consider in a particular study and for identifying relevant data sources.

Alcoholism↗
PubMed1996

Patterns and risk factors for sprains and strain in Ontario, Canada 1990: an analysis of the Workplace Health and Safety Agency data base.

This study presents the results of analyses performed to generate hypotheses concerning the general patterns of risk factors for occupational sprains and strains, using Ontario workers' compensation data housed in the Workplace Health and Safety Agency (WHSA) data base. Historically, the largest percentage of lost-time injuries in Ontario, Canada, have been sprains and strains. In 1990, there were 171,047 compensated lost-time injuries with a known nature of injury, of which 50.43% were sprains and strains. From cross-tabulations, a number of statistics such as odds ratios (ORs), 95% confidence intervals, P values, attributable risks and number of injuries attributable, were calculated. Results indicate that occupational sprains and strains are related to the time of the day and, in particular, time into the workshift. They occur more frequently than expected (based on the occurrence of non-sprain and non-strain injuries) in the morning hours and in the first 4 hours of the workshift. They are not found to be related to the starting or ending time or the length of the workshift. They occur more frequently than expected during the early part of a week, especially on Mondays, and the early part of a year (January to May). With respect to age, workers 30 to 59 years old have an increased risk of sprains and strains, whereas workers less than 30 years of age, or 60 or more years of age, have a decreased risk. Workers who are not single, and female workers, have a higher risk of sprains and strains than expected. With respect to occupations, nurses and truckers have a higher-than-expected risk. A number of work environments and activities, such as overexertion, bodily reaction from involuntary motions, running and stretching, and slippery surfaces, are associated with a high risk of occurrence of sprains and strains. These results suggest that significant reduction in the number of occupational sprains and strains could be achieved by targeting prevention programs to reduce excess risks encountered in the first 4 hours of the workshift, on Mondays, and during the first 5 months of the year, and by workers 30 to 59 years of age, female workers, and nurses and truck drivers. It is estimated that, with proper interventions to avoid sprains and strains, a large percentage of sprain and strain injuries could be avoided each year: ie 82.49% of injuries due to bodily reaction from involuntary motions, 89.43% of overexertions in lifting objects, 84.64% of running, stretching, and related injuries, and 76.64% of injuries resulting from loss of balance on slippery surfaces. This study uses an internal comparison, ie comparing the risk of sprains and strains to the risk of all other injuries for various risk categories of interest. As a result, an increased OR may mean an increased risk of sprains and strains, or it may mean a decreased risk of all other injuries for a particular risk category. There are also limitations in the use of workers' compensation data base for epidemiologic studies. Therefore, findings in this study are only suggestive for further investigations and should await confirmations before prevention programs are designed.

Accidents, Occupational↗
PubMed1996

Recording, notification, compilation, and classification of statistics of occupational accidents and diseases: the Thai experience.

An International Labour Organization (ILO) project was conducted in July and August 1995 in Thailand to assist with the development of an information system on occupational accidents and diseases for the Workmen's Compensation Fund (WCF). The WCF provides cash benefits and medical care to insured workers who suffer employment injuries. The project included literature research based on the facilities of the ILO in Bangkok, and those of the Thai government, and a thorough review of the ILO Code of Practice (the Code) on recording and notification of occupational accidents and diseases, and of other international recommendations on statistics of occupational accidents and diseases. A comparative study of various notification systems of occupational accidents and diseases in Australia, Canada, the Philippines, Sweden, Thailand, and the United States was conducted. The project also included fact-finding sessions among various information suppliers and users in Thailand. The Thai notification form for collecting data for the database was redesigned and pretested. Results of the project indicated that the Code is appropriate for the recording and notification of occupational accidents and diseases in Thailand. In addition, a number of information requirements, which were included in the notification systems in the countries studied but not listed in the Code, were found to be useful for the database. A list of the baseline variables to be included in the proposed database was developed, the notification form was redesigned, and coding schemes for the information collected on the redesigned form were constructed on the basis of international standard classification systems for economic activity, employment status, occupation, nature of injury, occupational disease, body part, type of accident, and agency. A number of mechanisms were suggested for cross-checking the accuracy of data in the database. Based on the review of the Code and other international recommendations on statistical reporting, a list of baseline statistics was formulated for inclusion in the WCF annual report. Lastly, some suggestions for future statistical analysis of the database were given.

Accidents, Occupational↗
PubMed1996

Health and social costs of tobacco use in Ontario, Canada, 1979 and 1988.

STUDY OBJECTIVE: This study aimed to estimate the health and social costs of tobacco use in Ontario, Canada. DESIGN: This was a cost-benefit analysis based on cross sectional data in 1988, stratified by age and sex, using an attributable risk model. The total cost of the consequences of tobacco use in the society included those costs attributed to extra deaths, disability, hospitalisation, physician visits, and fire losses, from tobacco use. PARTICIPANTS: The general population of Ontario, Canada. MAIN RESULTS: The total cost of tobacco use in Ontario, Canada in 1988 was estimated to be $3.623 billion--$721 million more than the total customer expenditure on tobacco products. Tobacco use was also found to be responsible for 14% of all adult deaths, 5% of all adult disability days, 14% of all days of hospitalisation, and 3% of all physician visits. Compared with previous results for Ontario (1979) the cost of the consequences of tobacco use had increased by about 25% and consumer expenditure by about 35% over the period, while the excess of consequences over expenditure fell slightly by about 3%. CONCLUSIONS: The annual excess of the social costs of tobacco use over total consumer expenditure is staggering. It is suggested that similar cost-benefit analysis of smoking be carried out at regular intervals to monitor smoking trends in the society, to estimate health and social costs, and to provide information for the setting of targets for tobacco control and healthy public policies.

Adolescent↗
PubMed1996

Diagnostic tests.

Explore the source record for details and available documents.

Carcinoma, Squamous Cell↗
PubMed1996

A nested case-control study on alcohol drinking, tobacco smoking, and cancer.

A nested case-control study was conducted to investigate the effect of alcohol consumption and tobacco smoking on cancers of various sites. The study population was based on 887 cases and 1774 controls, selected from a cohort of 17,200 male participants of a gastric mass survey in 1984, who were followed up for 9 years by the Chiba Cancer Registry, Japan. The odds ratio (OR) of colon cancer was significantly elevated in alcohol drinkers of one cup of sake-equivalent (27 ml ethanol) per day (OR = 3.5), and three cups of sake-equivalents per day (OR = 3.2) compared with nondrinkers, but its dose-response was not clear since two cups of sake-equivalents per day had an OR of 1.9, which was nonsignificant. Cancer risk elevation was especially predominant in the proximal colon, again showing no dose-response: OR = 30.7 for one cup of sake-equivalent per day, OR = 12.4 for two or more cups per day. Lung cancer showed a dose-response relationship with alcohol consumption, independent of tobacco smoking. A synergistic effect of alcohol intake and tobacco smoking was observed for upper aerodigestive tract and bladder cancer. Both alcohol drinking and tobacco smoking were found not to be associated with stomach cancer.

Alcohol Drinking↗
PubMed1996

Risk assessment in dentistry: health risks of dental amalgam revisited.

This paper reviews the basic methodology of risk assessment and describes the four steps involved, namely hazard identification, hazard evaluation, exposure evaluation, and risk estimation. The risk posed by the release of mercury vapor from dental amalgam restorations is used as an example to demonstrate the advantages and limitations of this process.

Adolescent↗
PubMed1995

Application of urinary mutagen testing to detect workplace hazardous exposure and bladder cancer.

The objectives of this biochemical epidemiologic case-control study were to evaluate urinary mutagen testing for occupational exposure assessment, and for possible screening for bladder cancer in the workplace. Thirty-seven patients (19 bladder cancer cases and 18 controls) completed a questionnaire. Two urine samples, i.e. a work sample taken while at work, and a home sample, were requested from each patient. Twenty-six patients (17 cases and 9 controls) gave a total of 47 24-h urine samples for mutagenicity testing by the Ames test. A positive Ames test was found to be associated significantly with current occupation with hazardous exposure (odds ratio = 3.7, 95%CI 1.1-12.9), and non-significantly with bladder cancer (odds ratio = 1.8, 95%CI 0.5-7.1). Our results show that the urinary Ames test has the potential of being used as a surveillance for current workplace hazardous exposure (sensitivity = 52%, specificity = 77%, positive predictive value = 72%, negative predictive value = 59%, positive likelihood ratio = 2.3), but not as a screening test for bladder cancer cases (sensitivity = 42%, specificity = 71%, positive predictive value = 3%, negative predictive value = 98%, positive likelihood ratio = 1.5).

Adult↗
PubMed1995

Cancer mortality among Chinese migrants: a review.

BACKGROUND: Epidemiological studies of cancer among migrant groups are beneficial in that they can provide insight into genetic and environmental factors in disease aetiology. Seven studies in the epidemiological literature have examined cancer mortality in migrants from China; methodological features and findings, which display remarkable consistencies between studies, are reviewed here. METHODS: Papers were included that compare site-specific cancer mortality patterns in first and second generation migrants to the experience in the host regions using vital statistics and census data. Rates had to be standardized either indirectly (using age-specific rates from the host regions) or directly (using a standard age structure) and standardized mortality ratios (SMR) or rate ratios (RR) were calculated. RESULTS: Migrant males had overall mortality from cancer that was often in significant excess compared to the host experience; results for females (for overall cancer) were equivocal. Both sexes had large and significant excess mortality from nasopharyngeal and liver cancer; SMR and RR were also consistently elevated for cancers of the stomach and oesophagus. There was notable attenuation in the high risk at these four sites in the second generation. All studies reported pronounced and significant reduced risk for prostatic cancer and female breast cancer, with little or no increase in mortality in the second generation. The SMR and RR also tended to be below unity for brain, bladder and kidney cancer. CONCLUSIONS: The results of this review indicate that cancer risk at several sites among Chinese migrants appears to be in transition, and that these findings are consistent across studies.

Canada↗
PubMed1994

Cell type identification in leukemia: the level of agreement among four independent diagnostic methods.

The level of agreement among four independent diagnostic methods for cell-type identification in leukemia was examined. The four diagnostic methods were routine morphology, electron microscopy, cell surface marker analysis by flow cytometry, and cancer cytogenetics. Sixty-five blood and bone marrow samples from fifty-seven patients were independently investigated by the four methods. It was found that when all cell-type categories were taken into consideration, overall percentages of agreement for pairs of the four diagnostic methods were poor, ranging from 43% to 67%. The kappa statistics, which correct for the agreement expected by chance, were also calculated. These kappa statistics had a range from 0.17 to 0.40 when all cell-type categories were taken into consideration, again indicating poor agreement between the methods pairwise. When each cell type was considered separately, much of the observed agreement was found to be expected on the basis of chance, as indicated by many of the kappa statistics being 0.00. For all categories, overall agreement for all four methods was poor and statistically significant, after correcting for chance (kappa = 0.20, (p = 0.000046). The poor agreement found among the four diagnostic methods indicates the need for further validation studies.

Cytodiagnosis↗
PubMed1993

Use of surnames to identify individuals of Chinese ancestry.

The objectives of this study were to develop and test surname lists for identifying Chinese ancestry. The Ontario all-cause mortality database for the period 1982-1989 was randomly split into source and test data sets. Frequencies by birthplace were compiled for each surname in the source data set, by sex, and the surnames were weighted based on their positive likelihood ratios. Lists of Chinese surnames were then assembled based on varying cutoff levels, and screening performance indicators for each list were calculated, including sensitivity, specificity, positive and negative predictive values, post-test odds, positive likelihood ratio, and yield. The internally generated lists were evaluated in the test data set. Results indicated that surnames have a good potential to identify individuals of Chinese origin. In the source data set, at a cutoff level of 100 for males (217 surnames) and females (210 surnames), both sensitivity and the positive predictive value of the surname lists for males and females were very high, above 80%, and the positive likelihood ratio was above 600. In the test data set and using the same surname lists, the sensitivity, positive predictive value, and positive likelihood ratio remained at a high level: 73%, 81%, and 603, respectively, for males; and 73%, 84%, and 772, respectively, for females. Various scenarios and their methodological implications are discussed.

China↗