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Biomedical subjects

C P Wen

Publications and source records attributed to C P Wen.

At least 19 recordsLinked to original sources
PubMed1996

A 50-year mortality follow-up of a large cohort of oil refinery workers in Texas.

To investigate further the possible role of occupational exposures on mortality, an update of a large Texas petroleum refinery cohort was undertaken. Between 1937 and 1987, 6799 deaths were identified among 17,844 employees. Relative to the general population of Texas, the overall standardized mortality ratio (SMR) showed a statistically significant deficit, as did nine other cause-of-death categories. Statistically significant mortality excesses were found for bone cancer (SMR = 207.8: 95% confidence interval [CI], 110.6 to 355.3), acute lymphocytic leukemia (ALL) (SMR = 259.6; 95% CI, 112.1 to 511.5), and benign/unspecified neoplasms (SMR = 194.9; 95% CI, 129.5 to 281.7). However, none of these diseases demonstrated an exposure-response relationship with length of employment. Subcohort mortality analyses by sex and race groups, length of employment, interval since hire, period of hire, and pay status were also performed. Overall, the update findings do not indicate that any excess mortality occurred as a result of employment at the refinery.

Cause of Death↗
PubMed1994

The health impact of cigarette smoking in Taiwan.

This study examined mortality attributed to active and passive smoking in Taiwan for the years 1981 and 1990. It was estimated that 19,283 deaths, representing 19% of the total number of deaths in 1990 (almost one out of five deaths in Taiwan), were smoking related. On an average day, 53 people died as a result of cigarette smoking, including 13 deaths from passive smoking. More men died (14,140 deaths) from smoking-related causes than from all cancer deaths combined (13,161 deaths); 91% of lung cancer and 30% of all cancers were due to smoking. In comparison, the smoking attributable mortality was much less for women, with 5,143 deaths. In addition, almost 5,000 deaths can be attributed to passive smoking every year in Taiwan with more deaths from women than from men. The overall prevalence rates for cigarette smoking has changed little in the last 20 years; approximately 60% for men and 4% for women although a consistent increase of one million new smokers was added every decade. Among younger people, the rate increased substantially, while it dropped 10-15% among middle-aged and older persons. Smoking is the largest single source of health risk in Taiwan. It is crucial that strategies to prevent smoking initiation among young people be developed so that the most vulnerable group can receive immediate attention. Despite the recent aggressive smoking cessation campaign by the Department of Health, much work remains. In order to facilitate this work, it is therefore recommended that the government commit to a goal of smoke-free nation by the year 2010.

Adolescent↗
PubMed1992

The standardized mortality ratio and life expectancy.

This paper develops a theoretical relation between the standardized mortality ratio (SMR) and the expected years of life and establishes a regression equation for easy conversion between these two statistics. The mathematical expression of the derived relation is an approximation, requiring an assumption of constant age-specific mortality ratios. It underestimates the "true" value calculated based on life table technique when the age-specific mortality ratios increase with age. This equation provides a conservative method to estimate the expected years of life for cohort mortality studies and facilitates an assessment of the impact of work-related factors on the length of life of the worker. It also allows one to convert the SMR to life expectancy in smaller studies whose sole objective is to determine the SMR in a working population. A 1% decrease (or increase) in the standardized mortality ratio will result in 0.1373 years increased (or decreased) life expectancy based on white male data for the US population. Furthermore, with data from 14 large oil refinery and chemical worker cohorts of white males, the "derived" expected years of life based on the regression equation closely predicts the corresponding value calculated using a standard life table technique. This statistical equation is expected to have practical applications when used in conjunction with the SMR to provide an approximate measure of life expectancy, a term and statistic familiar to most lay people.

Adult↗
PubMed1991

Mortality trend in a rapidly developing economy in Taiwan. Part II: Life expectancy and "potential years of life lost".

Taiwan has made remarkable economic progress in the last 30 years. The life expectancy of its population improved steadily during this period. A male child born in 1983 could look forward to 70.4 years of life and a female child to 75.3 years, gains of 17.5 years and 19.0 years, respectively, since 1950. The potential gains in life expectancy of the Taiwan population are also examined if the five leading causes of death are reduced or eliminated. In addition, this paper discusses the concept of potential productive years of life lost (PYLL), examines the leading causes of premature death and shows how this measure can be used to target prevention programs and health care planning.

Adolescent↗
PubMed1989

Mortality trends in a rapidly developing economy in Taiwan. Part I: Comparison with the USA and Japan 1976-1983.

The mortality experience of Taiwan was examined for two time periods (1976 and 1983) to determine the magnitude and direction of change in age-adjusted mortality and to identify deviation from the expected progress by comparison with two industrialized nations, the USA and Japan. Between 1976 and 1983 the overall mortality showed an annual average of nearly 2% decrease, mostly contributed by the marked reduction in the number of young. Significant reductions were also observed for deaths from strokes, rheumatic heart disease, ill-defined conditions, cancer of the stomach, and infectious diseases such as tuberculosis. A disturbing increase in suicide as well as accidents primarily caused by motor vehicles was noted. In general, cancer increased, to an alarming degree for environmentally implicated cancers such as lung, pancreas, nasopharynx, brain and liver in men. When compared to that of the USA or Japan, the mortality experience of Taiwan showed the following increases: overall female mortality, accidental deaths, suicide among elderly women, deaths from strokes, ulcers, asthma, and liver, nasopharyngeal and cervical cancers. However, the overall cancer mortality rate was still much lower than that either in the USA or Japan. Despite marked reductions in infectious disease mortality, deaths from tuberculosis were nearly 40 times those of the USA. Although deaths from ill-defined conditions decreased by half during this study period, they were still high, particularly among elderly women (13% of all deaths and 22 times higher than the USA), which probably reflects inadequate medical services for women. The role of the Taiwanese government in the financing of health services was found to be far smaller than that of the USA or Japan. Expanding health care expenditure by the government is desirable if improvement in the maldistribution of medical services is to be achieved and the untoward health effects of rapid industrialization is to be reduced.

Adolescent↗
PubMed1986

Long-term mortality study of oil refinery workers: V. Comparison of workers hired before, during, and after World War II (1940-1945) with a discussion of the impact of study designs on cohort results.

The mortality experience of a large refinery cohort (1937-1978) was examined by dividing it into three subcohorts according to hire dates: those hired before 1940, those hired during the period 1940-1945, and those hired after 1945. These three periods are approximately equivalent to before, during, and after World War II and span a total hiring period of more than 75 years. The results showed that a substantial portion of the cohort (3,330 or 27%) had been recruited during 1940-1945, and they contributed 980 or 28% of the total deaths. However, their mortality experience was quite different from the rest. A series of significant increases were seen among the external causes for accidents, suicide, and homicide. In terms of overall mortality and in contrast to the rest of the cohort, no "healthy worker effect" was seen (SMR = 1.00). They also showed increases in several types of cancer including cancers of the pancreas and prostate and leukemia. These unusual experiences cannot be explained either on the basis of their war-related deaths or on their period of employment (one-half were terminated within 1 year from date of hire), and data is insufficient to separate the role of hiring practices or their socioeconomic status. However, their life-styles were probably quite different judged from the fact that alcoholism-related deaths were increased as much as fivefold. Almost two-thirds of the total deaths occurred among 4,080 workers in the before 1940 subcohort. Further, the 5,117 workers of the after-1945 subcohort contributed only 5% of the total deaths. Thus, the results of the original refinery cohort (1937-1978) primarily reflect the experience of those employees hired before 1940. Given the same cohort method (historical prospective), cohort results vary widely according to different study designs, and this has implications for "generalizable" risk assessment or risk projections. A prospective study of new hires with 30 years of follow-up is rather inefficient because it would yield only a small number of deaths, with a strong healthy worker effect. The same is true for studies based on active workers with a short period of follow-up. Studies based on time of hire, however, provide a means for controlling time-related occupational exposures.

Accidents↗
PubMed1986

A review of methodological issues of the standardized mortality ratio (SMR) in occupational cohort studies.

This paper is a review and clarification of methodological issues related to the standardized mortality ratio (SMR), widely used in occupational epidemiology. Although the SMR seems to be a simple statistic, it can be misused and misinterpreted. The paper discusses SMRs in relation to age-specific mortality ratios, relative risk, life expectancy, and statistics derived from direct standardization. Inter-SMR comparisons and the effect of the choice of the comparison population on the SMR are also discussed. Mathematical and empirical review of SMR use has led to the development of a correction procedure which permits direct comparisons of two SMRs by adjusting for the age distributions of the two populations. The paper also proposes a method for testing the trend of age-specific mortality ratios (MRs). If MRs are homogeneous, this method can also be used to compare two SMRs. If MRs are not homogeneous, the relative risk between two sets of age-specific MRs can be tested for significance, but no summary index, including the SMR, can accurately describe the mortality experience over the entire age range. It is suggested that the summary statistics of a cohort mortality experience should include relative risk, attributable risk, and life expectancy. These statistics are complementary and can be derived or approximated from the data that generated the SMR. A valid risk assessment should weigh the evidence from all three summary statistics.

Adult↗
PubMed1985

Long-term mortality study of oil refinery workers. IV. Exposure to the lubricating-dewaxing process.

A retrospective cohort mortality study of 1,008 male oil refinery workers who ever worked on the lubricating-dewaxing process of the lube oil department and who have been followed for a period of 43 years is presented. These workers were exposed to a number of solvents, primarily methyl ethyl ketone [(MEK) CAS: 78-93-3] and toluene (CAS: 108-88-3), but at levels far below the current Occupational Safety and Health Administration's standard. The standardized mortality ratio (SMR) for all causes (0.70) and the SMR for cancer (0.86) are much lower than unity when they are compared to the mortality experience of the U.S. population. Also observed in this study were 8 prostate cancer deaths (4.4 expected) with an SMR of 1.82, which was not statistically significant (P = .16). Seven of these 8 prostate cancer deaths occurred among nonwhite males, who showed an SMR of 2.47 (P = 0.53). However, only 1 prostate cancer death was seen among workers specifically assigned to the MEK units. The remaining deaths occurred among maintenance workers who had lube oil department-wide assignments. This cancer risk increased with increasing duration of employment in the lube oil department. A latency of 20 years or more was also observed for these prostate cancer deaths. In this study the processing of lubricating oils was found to be at least as important as the MEK solvents, and department-wide maintenance workers were as much at risk as the MEK unit workers. In view of this finding and findings obtained by others, it seems prudent to continue to study lubricating-dewaxing process workers, including the medical monitoring of all such workers for prostate cancer.

Butanones↗
PubMed1984

The impact of competing risks on relative risks in occupational cohort studies.

This paper develops a method for adjustment of competing causes of death in the calculation of relative risk. It has identified three factors determining the significance of competing risks: (1) the magnitude of the overall mortality risk of the study population; (2) differential risk (or the adjustment factor) for mortality other than cause of interest between two populations; and (3) age intervals used in the mortality calculation. Thus, the impact of competing risks is increased if the study cohort has a high mortality risk, if the mortality other than the cause of interest has a large differential risk or if the mortality calculation uses wide age intervals. Two examples from a refinery cohort and the US national population show that among certain age groups unadjusted for competing risks the relative risk is overestimated by 9%. The impact of competing risks in these two particular examples is relatively small. Furthermore, if relative risk is expressed in terms of the ratio of mortality rates, competing risks can be ignored.

Aged↗
PubMed1984

A quantitative evaluation of competing risks in occupational studies.

Mortality risk is competing because each individual is subject to several competing causes of death but can only die from one. Adjustment for competing risks will allow more meaningful comparisons of cause-specific mortality of two populations, especially if dying from all other causes is significantly different between the two populations. In this paper, a method has been developed for adjustment of competing causes of death in the calculation of relative risk. It identifies three factors as determining the significance of competing risks: (1) magnitude of the overall mortality risk of the study population; (2) differential risk or adjustment factor for all other causes between two populations; and (3) age interval used in mortality calculation. Thus, the impact of competing risks is increased if the mortality risk of the study population is high, if the differential risk for all other causes is large or if wide age intervals are used in the mortality calculation. An example from refinery cohort data shows that in certain age groups unadjusted for competing risks the relative risk is overestimated by 9%. The impact of competing risks in this particular example is relatively small.

Age Factors↗
PubMed1984

Long-term mortality of oil refinery workers. II. Comparison of the experience of active, terminated and retired workers.

In occupational epidemiology a retrospective cohort study normally includes active, terminated, and retired employees and the mortality results may vary considerably if any of the three groups is excluded from the study. From a large refinery cohort of 12,526 white male workers followed between January, 1937 and January, 1978, the mortality experience of three groups (the active, terminated and retired) has been examined; detailed results, along with the merits and problems of studying these groups separately, are presented. The standardized mortality ratios (SMRs) for all causes are 0.68, 1.04 and 0.89 for the active, the terminated and the retired, respectively, and for all cancer, 0.85, 0.98 and 1.05. Significantly decreased SMRs are seen for most of the causes among the active and may be attributed to the "healthy worker effect." Exclusive study of active workers, although it may yield certain useful information, particularly on diseases of the young and those with short latency periods, is primarily a study of the healthy worker effect. Many favorable effects of the active worker will be encountered. The retirees as a whole experienced no significant excess mortality for any causes, although examination of a subgroup, the early retirees, did reveal a significant excess of deaths from diseases of the nervous system and sense organs. The retired may appear to be an ideal group for study because they usually have worked for an extended period of time, they may have experienced long-term occupational exposure and they have lived long enough to develop diseases with long latency periods; however, serious problems arise from studying only the retirees and these are discussed. The terminated group contributed 41% of the person-years, 49% of the total number of individuals and 38% of the deaths and is far too important to be omitted. Contrary to previous reports, the terminated did not demonstrate a significantly adverse mortality experience when compared with the general population, although they did not show the healthy worker effect that was seen among the active.

Adult↗
PubMed1984

A result-oriented medical information system. An alternative to the conventional approach.

A result-oriented medical information system at the Gulf Oil Corporation is described. Mortality data acquired mostly from routine company operations have been used to calculate standardized mortality ratios (SMRs) and life expectancy. Results show that male employees at the age of 20 have a life expectancy of 74.8 years. Compared with the U.S. general population at age 20 with a life expectancy of 71.8 years, Gulf employees have an advantage of exactly three years. Such an advantage may seem small, but it is equivalent to the gain that could be achieved if all deaths from cancer were eliminated in the United States, a hypothetical and impossible situation. These life expectancy data have the potential for use by the company to influence insurance premiums traditionally set by life insurance companies as well as to aid in the management of the company's pension fund. The SMR for all causes for the male employees is 0.82, significantly decreased in comparison with that of the U.S. general population. This favorable experience has been referred to as "the healthy worker effect." Cause-specific SMRs show a generalized pattern of deficits, some of which are statistically significant. None showed a significant increase. Seventy-six percent of the male deaths occurred among employees aged 65 years or older. If these annuitants (those alive at the beginning of the study) were not included and only the active workers were studied, an SMR of only 0.54 would be obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Absenteeism↗
PubMed1983

Long-term mortality study of oil refinery workers. I. Mortality of hourly and salaried workers.

This longitudinal study examined the mortality and cancer experience of workers at the Gulf Oil refinery located in Port Arthur, Texas. The cohort was studied over a period of 41 years, from 1937 to 1978, and consisted of 16,880 employees, with an accumulation of 406,198 person-years; 4361 deaths were observed. Emphasis of this study was placed on the experience of the hourly and salaried male workers employed one day or more and those with a minimum of one year employment. The standardized mortality ratio analysis revealed generally favorable mortality experience of the refinery workers, including that of overall cancer. Statistically significant deficits in mortality were found for several cancer sites including bladder, liver, and esophageal cancer. Many of the increased cancer risks suggested in the literature were not confirmed in this study. Although bone cancer was found to be increased significantly, review of those death certificates raises questions as to the accuracy of the recording and coding of this cancer. Sample size of this study is capable of providing sufficient statistical power for the detection of a twofold increase in mortality risk for many cancers, if such risk exists.

Adult↗
PubMed1983

Retrospective mortality and medical surveillance studies of workers in benzene areas of refineries.

The mortality and health experiences of refinery workers employed in benzene processes or operations are described. A retrospective cohort mortality study of benzene workers employed from 1952 to 1978 revealed no excess in overall general mortality or in cancer mortality compared either with the experience of the U.S. general population or with that of an internal control group. Ascertainment of vital status was accomplished for 99% of the cohort. Recent industrial hygiene data that included 1,394 personal samples indicated that 84% of all benzene exposures were less than 1 part per million (ppm), with a median exposure of 0.14 ppm for the refinery workers, and 0.53 ppm for those in the benzene-related units. Among these workers, no deaths from leukemia were observed. A medical surveillance program for benzene workers is also described, with special emphasis on the effectiveness of laboratory screening. Evaluation of data for a 21-year period showed no significant changes in the blood indices of the workers as a group. The limited value of establishing screening guidelines without the support of epidemiological studies is discussed.

Adult↗
PubMed1983

Anatomy of the healthy worker effect: a critical review.

The healthy worker effect is the composite result from factors such as (1) selection of the work force, (2) changes in lifestyle accompanying employment, and (3) methodological characteristics of the standardized mortality ratio (SMR). While the choice of the general population as the comparison population is the underlying reason for this effect, no more feasible, widely accepted or "better" alternative is yet available. Much of the current understanding of the healthy worker effect has been limited to an examination of selection of the work force. The purpose of this report is to illustrate, using examples from a large cohort study, the importance of many factors other than selection. They include employment-associated benefits such as economic gain, medical insurance and lifestyle changes, the proportion of active workers, the calculation method, data completeness, length of follow-up and certain characteristics of SMR methodology. It is shown that some of the healthy worker effect is characteristic of SMR methodology and that the strength of the healthy worker effect depends on the proportion of active workers in the cohort. Furthermore, the disappearance of the healthy worker effect may be due to factors such as aging of the cohort and can be totally unrelated to the true increase in the mortality risk. In other words, its disappearance, in many instances, may be an artifact of SMR methodology.

Adult↗
PubMed1982

Anatomy of the health worker effect - a critique of summary statistics employed in occupational epidemiology.

The "healthy worker effect," perhaps more accurately termed the "active worker effect" has been acknowledged by numerous investigators who have disregarded its significance. The healthy worker effect is expressed by SMRs (standardized mortality ratios) and influenced by the following three factors: (i) selection bias, (ii) improved socioeconomic status, and (iii) the conventional way of calculating SMRs. An examination of these three factors shows that selection for "employability" is probably the most significant factor for the healthy worker effect. For example, the shorter the observation, the smaller the SMR, and the stronger the health worker effect. Secondly, improved socioeconomic status as a result of employment has been shown to lower mortality. Last, although the SMR has the advantage of estimating relative risk in a small sample, it suffers many methodological pitfalls. It is recommended that at least three parameters be used to summarize mortality experience among the employed: (i) relative risk, (ii) attributable risk, and (iii) life expectancy.

Employment↗