Korean J Prev Med.  1999 Dec;32(4):452-458.

A Cohort Study on Risk Factors for Chronic Liver Disease: Analytic Strategies Excluding Potentially Incident Subjects

• Lee MS
• Kim DS
• Kim DH
• Bae JM
• Shin MH
• Ahn YO

Abstract

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 diseased group(n=2,217) when they were HBsAg positive, serum GPT levels higher than 40 units, or had or has liver diseases in baseline surveys. Cox' 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 disease onset. The analytic strategy excluding potentially diseased subjects was considered appropriate for identifying risk factors for chronic liver diseases.

Keyword

Cohort studies; Liver diseases; Epidemiology; Cox regression; Bias

MeSH Terms

Bias (Epidemiology)
Coffee
Cohort Studies*
Surveys and Questionnaires
Death Certificates
Drinking
Epidemiology
Hepatitis B Surface Antigens
Incidence
Insurance
Life Style
Liver Diseases*
Liver*
Medical Records
Obesity
Odds Ratio
Risk Factors*
Smoke
Smoking
Soybeans
Coffee
Hepatitis B Surface Antigens
Smoke