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Biomedical subjects

B C Choi

Publications and source records attributed to B C Choi.

At least 19 recordsLinked to original sources
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↗
PubMed1993

Characterization of a peroxidase in excretory-secretory product of adult Paragonimus westermani.

When activity of peroxidase in adult Paragonimus westermani was monitored using o-dianisidine and H2O2 as substrates, its specific activity was 1.5 times higher in excretory-secretory product (ESP) than in crude extract. The enzyme was purified by two purification steps of Sephacryl S-300 Superfine gel permeation and DEAE-Trisacryl M anion exchange chromatographies. Its activity increased 16.9 fold with 32.3% recovery. The enzyme was inhibited totally by 1 millimoles of dithiothreitol (DTT), 2-mercaptoethanol and azide. Molecular mass was 16 kDa in reducing SDS-polyacrylamide gel electrophoresis (PAGE) or 19 kDa in TSK-Blue gel filtration high performance liquid chromatography (HPLC), respectively. Special staining for peroxidase by diaminobenzidine on SDS-PAGE confirmed the activity. The peroxidase was less reactive to a paragonimiasis serum when observed by SDS-PAGE/immunoblot. In addition, specific activities of superoxide dismutase (SOD) and catalase were also identified in the ESP. High activities of these antioxidant enzymes in ESP indicate that they are parts of defense mechanisms against reactive oxygen intermediates from host.

Animals↗
PubMed1992

Antibody drug carrier for immunotherapy of superficial bladder cancer: ultrastructural studies.

Superficial bladder cancer represents a promising target for intravesical, antibody-guided therapy. The construction of an optimum antibody-cytotoxic drug conjugate depends mostly on the appropriate selection of a monoclonal antibody (mAb). We have used immunogold labeling and SEM to specifically map the distribution of antigens expressed on three bladder cancer cell lines and on the luminal surface of biopsies from human transitional cell carcinoma of various grades and from normal bladder mucosa. The 48-127 mAb, which recognizes a M(r) 54,000 surface glycoprotein (gp54), was found to be very promising as a potential drug carrier. This antibody reacts with the surface of cells from low- and high-grade tumors; it does not react with the normal urothelium. Labeling of normal bladder mucosa was observed, however, on microvillous intermediate urothelial cells occasionally exposed by small areas of desquamation. The 48-127 mAb could target drugs to all areas of transformed urothelium while avoiding drug delivery to the normal, undesquamated bladder mucosa. Kinetics of gp54/48-127/gold complexes were tested in vitro with T24 and RT4 human bladder carcinoma cell lines incubated in the presence of the 48-127 mAb directly conjugated with 17.7-nm gold particles. Internalization of the gp54/48-127/gold complex was readily demonstrated by transmission electron microscopy. These results suggest that the 48-127 mAb represents a valuable drug carrier for intravesical therapy, allowing specific tumor targeting and internalization of various cytotoxic agents.

Aged↗
PubMed1992

Sensitivity and specificity of a single diagnostic test in the presence of work-up bias.

A diagnostic test is put into routine use by being applied to a population with unknown test status and unknown disease status. All subjects with a positive test are then referred to a "gold standard" assessment for the disease. Subjects with a negative test are normally not referred to the "gold standard" assessment. In some cases, the investigators may refer a small random sample of subjects with a negative test to the "gold standard" assessment in order to determine if they really do not have the disease. If "gold standard" results are not available on an entire population, it is well-known that work-up bias, or sequential-ordering bias, exists. In this situation, classical equations for sensitivity and specificity give biased results. This paper describes an equation for estimation of prevalence, and two new equations which calculate sensitivity and specificity from prevalence and predictive values, and which are appropriate for data from this type of "irregular observational design".

Bias↗