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KMID : 0371019990320040452
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Journal of Preventive Medicine and Public Health
1999 Volume.32 No. 4 p.452 ~ p.458
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A Cohort Study on Risk Factors for Chronic Liver Disease : Analytic Strategies Excluding Potentially Incident Subjects
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Lee Moo-Song
Kim Dong-Hyun
Bae Jong-Myon
Shin Myung-Hee
Ahn Yoon-Ok
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Abstract
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Objectives : The authors conducted the study to evaluate bias when potentially diseased subjects were included in cohort members while analyzing risk factors of chronic liver diseases.
Methods : Total of 14,529 subjects were followed up for the incidence of liver diseases from January 1993 to June 1997. We have used databases of insurance company with medical records, cancer registry, and death certificate data to identify 102 incident cases. The cohort members were classified into potentially diseases group(n=2,217) when they were HBsAg positive, serum GPT levels higher than 40 units, or had or had liver diseases in baseline surveys. Cox´s model were used for potentially diseased group, other members, and total subjects, respectively.
Results : The risk factors profiles were similar for total and potentially diseased subjects : HBsAg positivity, history of acute liver disease, and recent quittance of smoking or drinking increased the risk, while intake of pork and coffee decreased it. For the potentially diseased, obesity showed marginally significant protective effect. Analysis of subjects excluding the potentially diseased showed distinct profiles: obesity increased the risk, while quitting smoking or drinking had no association. For these intake of raw liver or processed fish or soybean paste stew increased risk; HBsAg positivity, higher levels of liver enzymes and history of acute liver diseases increased the risk.
Conclusions : The results suggested the potential bias in risk ratio estimates when potentially diseased subjects were included in cohort study on chronic liver diseases, especially for lifestyles possibly modified after diseases onset. The analytic strategy excluding potentially diseased subjects was considered appropriate for identifying risk factors for chronic liver diseases.
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KEYWORD
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Cohort studies, Liver diseases, Epidemiology, Cox regression, Bias
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