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Volume 12 (1); June 1990
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Korean Society of Epidemiology
Korean J Epidemiol. 1990;12(1):101-106.
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Korean Society of Epidemiology
Korean J Epidemiol. 1990;12(1):100-100.
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Brief communication
Use of a SAS program for conditional maximum likelihood estimate in linear logistic model to fit pair matched data
Keun Young Yoo
Korean J Epidemiol. 1990;12(1):93-99.
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For the most valid estimation of matched odds ratios in the analysis of pair-matched data, the method of choice is the conditional maximum likelihood method. Many alternative methods have been suggested, but in most cases, they lead to biased estimations in comparison to the conditional maximum likelihood method. Despite developments in statistical software such as GLIM, EGRET, and EPILOG for conditional likelihood estimation, the applicability of the SAS program remains limited, although it is one of the most common and popular statistical computer programs. According to the modification suggested by Holdford, since the conditional probability of selection in pair-matched case-control studies approximately takes the form of a linear logistic model, a conditional likelihood estimate can be estimated using standard statistical software. In this study, the author introduces a simple SAS program using PROC LIFEREG, which is commonly used for survival function analysis, to estimate matched odds ratios.
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Original Articles
A study on the chronological changes of serologic markers of HBV infection among the school children in a rural community of Korea
Bo Youl Choi, Yeun Ho Lee, Ung Ring Ko
Korean J Epidemiol. 1990;12(1):81-92.
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In Korea, thr reported prevalence of HBsAg in apparently health persons varies as 7.5 to 13.3% in adults and 3.9 to 5.9% in school children. Suggesting, this country belongs to high prevalent area in the world. B hepatitis has been classified into acute and chronic, apparent and inapparent infection, and the prognosis of HBsAg chronic carrier is also variable from complete recovery to fatal outcome such as liver cirrhosis and primary hepatocellular carcinoma. In order to assess the status of infection accurately, the follow-up examination on HBV serologic markers for the considerable period is necessary. To study the chronological change of serologic markers of HBV infection, authors carried out three successive examinations on HBsAg(by RP-HA) and Anti-HBs(by PHA) of the school children in June, 1985, April 1986 and June 1987. Vaccinees was excluded in the analysis of data. The results are summarized as follows. 1. HBsAg positive rates in 1985, 1986 and 1987 were 5.89%, 5.67% and 4.29%, and Anti-HBs positive rates 9.68%, 16.75% and 13.50%, repectively. 2. The various chronological changes of serologic markers of HBV infection was observed. All 5 cases who became HBsAg positive in 1986 reversed to be HBsAg negative in 1987, suggesting the newly infected persons in this age group do not ordinarily turn to chronic carrier. Any Anti-HBs positive (58 cases) in 1985 and 1986 did not became HBsAg positives in the next years. So, it is confirmed that Anti-HBs has protective property to HBV infection. 3. Average incidence rate of HBV infection was 7.00(95% C.I.; 4.86-9.34) per 100 person-years. The rate showed a trend of increase as the age increased(5-9yrs; 4.87, 10-14yrs; 5.99, 15-17; 18.87), and the rate in male(8.80) was higher than in female(5.45). Average loss rate of Anti-HBs was 26.64(95% C.I.; 15.42-39.25) per 100 person-years. Period prevalence rate of HBsAg chronic carrier was 4.36%(95% C.I.; 2.18-6.85) and no sex difference was observed. The rate was highest(6.42%) in 5-9 years group and lowest(3.13%) in 10-14 years group, though statistically not significant.
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Recent trends of infant death rates and its determinants in Korea
Seung Hyung Han, Il Soon Kim
Korean J Epidemiol. 1990;12(1):57-80.
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The purpose of this research was to estimate the infant mortality rates in Korea and to determine related factors. For the study, data from the National Fertility and Family Health Survey conducted by Korea Institute for Population and Health in 1988 was analyzed. The units of analysis were all births that occurred after 1974 from 7922 married women. The specific objectives of this research were, firstly, to calculate annual infant, perinatal death rates by fiscal years, and secondly, to identify determinants of infant death by applying the proportional hazard model and logistic regression model. The results of the study are summarized below. 1. Infant death rates declined from 28.4 in 1974-1975 to 13.9 in 1984-1985, perinatal death rates from 28.2 to 15.3, and neonatal death rates from 19.8 to 11.2(rates per 1,000 births). 2. By applying the proportional hazard model and multiple logistic analyses to the data from all births after 1974, residence, parity, the experience of infant death, occupation and inter-birth interval were shown to be significant risk factors, while the data from the birth cohorts of 1980-1987 showed that only parity and residence were significant and their relative risks were above 2. By analyzing the data from the last births after 1983, parity, residence, inter-birth interval and occupation of the head of the household were shown to be significant and the relative risk of the vaccination status of children was 2.2 and proved to be the most important factor. To sum up the results, the infant death rates showed a steep decline during the period between the latter part of 1970's and the earlier part of 1980’s, mainly due to the rapid economic and social development of Korea and to the decrease in fertility caused by population control policies in the 1970's. Other effective health care policies expedited such a decline. After the middle of the 1980’s, the speed of descent seemed to slow down. Strong policies for maternal child health care are required in order to bring the level of infant death rates to 6, which are considered to be the lowest rates that can be achieved by modern medicine. One of the reasons why the infant death rates are still high in rural areas and in mothers of high parity can be explained by the fact that they belong to a higher risk group and have been excluded from maternal-child health care programs.
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Survival analysis of coal worker's pneumoconiosis by radiological findings
Kyung Yong Rhee, Gwan Hyeong Yi, Ho Keun Chung
Korean J Epidemiol. 1990;12(1):44-56.
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The authors investigated mortality rates and survival curves of coal workers’ pneumoconi-oses(CWP) in hospitalization by radiological findings with covariates, i.e.. age, emphysema, and pulmonary tuberculosis. Study subjects were composed of 738 patients entered the cohort in diffent years. There were differences in survival curves of CWP according to radiological findings controlled by the covariates. Mortality rate of large opacity group at five years was higher than that of small opacity group. The mortality rate of the group of irregular shape was also higher than that of rounded shape. There were differences in the pattern of survival curves of each group of profusion 1, 2, and 3 controlled by the covariates. In large opacity groups, A, B, and C, there were also differences in the pattern of survival curves.
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Controversy
Association between use of reserpine and breast cancer
Kwang Ho Meng
Korean J Epidemiol. 1990;12(1):38-43.
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Reserpine was being widely used as a well-established, beneficial treatment for hypertension, when three studies, published in 1974 in the same issue of the Lancet, suggested that reserpine users, compared with non users, had a threefold to fourfold increased risk of developing breast cancer. These results were subsequently contradicted by the results of nine other studies, published between 1975 and 1980. In a recent review of all those studies, the initial causal association was deemed erroneous, although the reasons for the falsely positive results were not identified. Recently, however, one study done by Horwitz and his colleagues in Yale University claimed that the false association might have been produced by a phenomenon called exclusion bias that were probably happened because patients with cardiovascular disease were rejected as possible controls in the original reserpine-breast cancer case-control study. This paper summarizes the results of those studies resulted in positive and negative associations between the use of reserpine and breast cancer, and reviews the methodological variations of the studies.
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Special editions
Adjustment of confounders on statistical inference: analysis using a statistical package
Won Chul Lee
Korean J Epidemiol. 1990;12(1):24-37.
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Controlling of confounders is one of the most important methodological issues in epidemiological studies because the associations of exposures and outcomes are very much influenced by confounders. Matching, stratification and multivariate statistical methods are frequently used to control the effects of confounders. This paper introduces two statistical package programs: Mantel-Haenszel method for stratification and logistic regression analysis for multivariate analysis. For explanation of the package programs, data on the association of body mass index with adenomatous polyp of colon in the United States was used.
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A review on some techniques to control the effects from confounding factor
Seung Wook Lee
Korean J Epidemiol. 1990;12(1):9-23.
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This paper is to review some methods available to control the effect from confounding factors when we conduct epidemiological studies. Basically, there are two approaches: 1) matching before data collection, and 2) statistical analysis after data collection. For matching, caliper matching, nearest available matching, stratified matching, frequency matching, and mean matching as univariate matching method are reviewed. Also, multivariate caliper matching, multivariate stratified matching, minimum distance matching, discriminant matching and linear adjustment matching as multivariate matching methods are explained. The standardization and stratification are introduced as methods for after-data-collection. Also various statistical techniques including log-linear method, logistic regression method, multiple regression method, and covariance analysis are illustrated for possible use in data analysis with confounding variables. Finally, analysis techniques for matched data with controls more than single are explained. We reviewed all theses techniques briefly, mainly on the logical meaning. Also, we reviewed the statistical techniques that will be used for analysis after the matched data are obtained.
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Confounder: concept and importance in epidemiologic research
Y.O. Ahn, B.J Park
Korean J Epidemiol. 1990;12(1):1-8.
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Epidemiol Health : Epidemiology and Health