Since genotypes are unchangeable, adjustment of prognostic effects in prevalent case-control studies may produce an unbiased estimate of odds ratio (OR) for disease occurrence. In this paper, the prognostic effects on OR is demonstrated, then three approaches to examine and/or adjust the OR are presented. The demonstration shows that the prognostic effects are larger in diseases with poor prognosis than in those with better prognosis. Genotypes increasing disease risk and fatality rate are underestimated, while those increasing the risk and improving prognosis are overestimated. The simplest approach to examine the OR derived from prevalent casecontrol studies is to conduct stratified analysis according to the interval between diagnosis and study enrollment. When the stratified analysis finds no substantial difference in the estimate, the OR reflects mainly the relative risk for disease occurrence. The proportion of genotype among putative cases at diagnosis can be estimated from prevalent cases by a logistic model, producing the OR adjusted for the interval from diagnosis. An incomplete-data case-control design is also applicable to adjust the prognostic effects. An actual prevalent case-control study on breast cancer is used to demonstrate the three approaches. They are useful to compensate the disadvantage of prevalent case-control studies. J Epidemiol, 2001 ; 11 : 204-210
The Japan Collaborative Cohort Study for Evaluation of Cancer Risk Sponsored by Monbusho (JACC Study) included in its self-administered questionnaires some single-item questions concerning physical activity. We examined the validity of the questions among 1, 730 Japanese adults and the reliability of the questions among 1, 075 Japanese adults. The validity of the sports and physical exercise questions was estimated by comparing the self-administered questionnaire responses with the time spent on the activity and the energy expenditure index for the previous 12-month period, elicited by the interviewing method used in the Japan Lifestyle Monitoring Study with a minor modification. The Spearman's rank correlation coefficients ranged from 0.43 to 0.60, showing moderate correlations. On the other hand, test-retest reliability was estimated by comparing the responses from two separate surveys conducted roughly one year apart. Weighted kappa coefficients of sports and physical exercise questions, classified according to sex and age, ranged from 0.39 to 0.56, showing moderate reliability; and those of a question about walking ranged from 0.25 to 0.39, showing fair reliability. We suggest that measuring physical activity level with these single-item questions may be appropriate for establishing baseline data that reflects long-term physical activity in a large-scale cohort study targeting lifestyle-related diseases. J Epidemiol, 2001 ; 11 : 211-218
This article examines whether an association is found between quantity of alcohol consumed and all cause mortality, and a relation is detected between types of alcoholic beverage and all cause mortality in Japanese male adults. A cohort study was performed in three towns located in two former coal mine areas and a rural area in Fukuoka. A mail survey was carried out between 1988 and 1990, and was extended in a follow-up period to 1995 (two towns) and 1999 (one town). 6, 652 Japanese men aged from 40 to 69 years responded to a questionnaire that included alcohol consumption and smoking habit. The data were analysed with Cox's proportional hazards model. As regards an association between all cause mortality and quantity of alcohol consumed, statistically significant relations were recognized in occasional drinkers and drinkers with less than 25g ethanol per day (hazard ratio= 0.71, 95% Cl: 0.50-0.99; hazard ratio= 0.51, 95% Cl: 0.29-0.88, respectively). With respect to drinkers with 25-50g/day and >=50g/day, no significant relation was observed in the risk for all cause mortality. Comparing all cause mortality for daily drinkers and nondrinkers with respect to the beverage types, a risk was lower for daily drinkers than for nondrinkers with every type of beverage studied. In particular, there was a statistically significant adverse association for all cause mortality among subjects who reported drinking Japanese sake compared with nondrinkers (hazard ratio= 0.45, 95% Cl: 0.30-0.68). Alcohol consumption (particularly Japanese sake) is likely to be associated with a reduced hazardous ratio of all cause mortality. J Epidemiol, 2001 ; 11 : 219-223
This study aims to determine if cigarette smoking is associated with engaging in other healthrisk behaviors among high school students in Japan. Self-administered anonymous questionnaires were conducted in 1999 using a sample of 1, 466 students (male: 50.5%, female: 49.5%) in grades 10 through 12 at seven public senior high schools in urban areas of Okinawa, Japan. Health-risk behaviors studiedal included cigarette smoking, alcohol drinking, thinner use, sexual intercourse, suicidal ideation, nonuse of seat belts, physical inactivity, and weight loss practices. In the logistic regression models, controlled for sociodemographic variables, smoking was significantly associated with all health-risk behaviors except physical inactivity. In particular, associations of alcohol drinking and sexual intercourse with smoking were strong. Among male students, statistically significant odds ratios existed for alcohol drinking, sexual intercourse, and nonuse of seat belts. Among female students, all of the odds ratios for health-risk behaviors were statistically significant, except for physical inactivity. Generally, the odds ratios of female students were higher than those of male students. In conclusion, high school students who smoked cigarettes in this study may be at higher risk for engaging in other health-risk behaviors. Particularly, alcohol drinking and sexual intercourse are more likely to co-occur with smoking. These findings suggest that smoking prevention programs should be integrated with other health-risk behaviors. J Epidemiol, 2001 ; 11 : 224-228
The interplay of physical activity and vitamin D receptor (VDR) gene polymorphism in their effects on bone mineral density (BMD) was studied for 120 Japanese girls aged 18-19 years. BMD at distal radius in the group with the VDR genotype at the Apal site of Aa was significantly higher than that in the as group, but this association disappeared in a group having the habit of physical activity. The Aa genotype gave a higher BMD than the as genotype only in the group without the habit of physical activity. The habit of physical activity was associated with a higher BMD only in the as genotype group. The similar interplay was observed in the VDR genotype at the Taql site. We thus suggest that physical activity and VDR genotypes affect BMD in independent mechanism to give a saturated level of BMD. Higher dietary calcium intake tended to be associated with higher BMD only in the Aa genotype, suggesting that the calcium intake and VDR genotype affect BMD in a synergistic mechanism. J Epidemiol, 2001 ; 11 : 22-232
The case subjects were 67 stroke patients (27 males and 40 females, mean age 65.7±7.1), who suffered from stroke attack and had participated in annual medical check-up between 1987 and 1988 at Oyabe Public Health Center. The controls, which were adjusted for sex, age and blood pressure level with the case subjects, were selected from participants attending their annual medical check-up in 1987-1988. The serum thiocyanate level of case subjects were significantly higher than that of controls (p<0.05). The usefulness of measurement of serum thiocyanate level as an indicator of smoking status was assessed by using multiple logistic regression analysis adjusting for body mass index, mean blood pressure, and serum cholesterol was found. An odds ratio of 3.00 (95% confidence interval: 1.06-8.48, p<0.05) in cerebral infarction. It is considered that serum thiocyanate may be useful as an indicator of smoking status to assess the relationship with stroke onset, especially for cerebral infarction. J Epidemiol, 2001 ; 11 : 233-237
We examined the effect of smoking cessation on natural killer (NK) activity of peripheral blood lymphocytes in terms of a prospective study of 27 Japanese subjects who participated in a smoking cessation intervention program. This program was delivered by means of groupcounseling offering 7 sessions of about 2 hours over 6 months to help smokers to discontinue the habit. Thirteen subjects ceased smoking (quitters), while 14 continued to smoke (cigarette smokers). NK activity before the intervention was correlated positively with age (correlation coefficient=0.46, P<0.05). NK activity remained almost constant among quitters, comparing the activity before and after the intervention, while it decreased among cigarette smokers although it was not statistically significant. In the subgroup analysis, NK activity increased among those aged less than 65 years, or urine cotinine levels over 800 ng/ml before the intervention, especially among quitters, but there were no statistical significances. Multiple regression analysis showed changes in NK activity were correlated significantly only with age (standard regression coefficient=-0.44, P<0.05). These findings suggest that smoking cessation intervention programs might have been more effective for younger than elder subjects in consideration of NK activity. J Epidemiol, 2001 ; 11 : 238-242
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