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Effects of Exposure-Confounder Misclassification and Criteria of Model Choice in Ecologic Studies.
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Sun Hee Lee, Chung Mo Nam, Hung Wok Park
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Korean J Epidemiol. 1996;18(2):142-150.
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Abstract
Ecologic studies are widely used in all fields of public health on account of accesibility of data. However, two problems related to these studies have been brought up. The first is ecological fallacy occurred in the course of interpreting the ecologic level of exposure-disease associations into individual level. The second is exposure isclassification which leads to serious bias. Nevertheless there is few methodologic study dealing joint effects of the two problems in ecologic study. This study was conducted to suggest an ecologic model not having an ecologic fallacy due to model linkage failure and a methodology for correcting the misclassification bias due to exposure-confounder misclassification. Finally, we suggest a criteria for the ecologic model selection. Main results are as follows: 1. A linear ecologic regression model has a serious ecological fallacy due to model linkage failure and the misclassification bias due to the exposure-confounder misclassification. 2. An interaction ecologic regression model has no ecological fallacy due to model linkage failure, but it is affected seriously by the exposure misclassification. However misclassification bias could be removed mathematically if the information related to the misclassification was known. 3. A log-linear ecologic regression model has an ecological fallacy due to model linkage failure. It is seriously biased as the individual risk ratio are increased, but relatively less affected by the exposure misclassification than interaction ecologic regression model. 4. One of the two ecologic regression model-interaction ecologic regression model and log-linear ecologic regression model- would be selected according to the information of individual risk ratio and exposure misclassification. But using a linear ecologic regression model should be avoided in any circumstance. The above results are only valid in case that there is no other source of ecological fallacy except model linkage failure. Also exposure and confounder are independent each other, measured binary, and having nondifferential misclassification. Since the above assumptions are somewhat strong in considering the real situations of ecologic studies, it is necessary to extend the scope of this study.
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Cholera in Korea, 1991: models of transmission.
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Han Joong Kim, Il Suh, Hee Choul Oh, Kyoo Sang Kim, Sun Ha Jee, Soon Young Lee, Sun Hee Lee
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Korean J Epidemiol. 1991;13(2):123-139.
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Abstract
In August-September 1991，Korea had a cholera epidemic caused by Vibrio El Tor Ogawa with 92 bacteriologically confirmed cases and 8 deaths.
Seochun-gun Choongnam, Kunsan-si and Okgu-gun Chunbuk area, which are located near the mid-west coast of the country, were mainly affected. Vibrio cholerae were isolated from sewage water, sea water, squid and shell-fish tested during the epidemic, and an epidemiologic study found that consumption of raw shellfish or fish was the most probable source of cholera infection.
Vibrio cholerae were thought to have spread from foreign countries and there were some evidence that an environmental reservoir of cholera might play a role in the transmission of cholera in this epidemic.
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Epidemiological characteristics of cholera epidemic in Korea, 1991.
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Hee Choul Oh, Jong Ku Park, Mook Shik Kim, Kyoo Sang Kim, Sun Ha Jee, Soon Young Lee, Sun Hee Lee
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Korean J Epidemiol. 1991;13(2):112-122.
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Abstract
From July 30th through September 9th, 1991, 188 cases of cholera were reported throughout most provinces in Korea. Of the cases 92 were bacteriologically confirmed and 96 were diagnosed by clinical symptoms. Through screening of the cholera epidemic area residents 58 inapparent infections were discovered and 8 deaths occurred.
A population interview survey was conducted to the people inhabiting the five villages at the two epidemic foci, Sochon and Okgu. Other various information sources such as reported cases to health centers or quarantine stations, medical records of some hospitals, and laboratory findings of National Institute of Health were used to describe the cholera epidemic. Data from these sources were rearranged and analysed on an individual bases. Epidemiological characteristics of the 1991 cholera epidemic of Korea are as follows:
1. Vibrio cholerae biotype El Tor, sero type Ogawa was the causitive agent.
2. The epidemic duration was 25 days from August 13th to September 7th.
3. Epidemiological investigation of the two epidemic foci-Sochon, and Okgu counties-in the west coastal regions of the Korean penisula-revealed that 155 cases occurred in explosive outbreaks amounting to 82.5% of the total 188 noted cholera cases.
4. The epidemic curve of the 1991 cholera epidemic showed that of a typical point-source outbreak suggesting that there were few secondary infected cases.
5. Lower incidence rates among younger age groups and higher incidence rates among older age groups were noted. These findings support that this cholera outbreak was epidemic not endemic.
These findings suggest that epidemiological characteristecs of the 1991 cholera epidemic differ from those of 1980 or before, in number of patients, duration of epidemic and the epidemic curve pattern. The authors suspect that improved national and personal hygiene might explain the difference.
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