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Objective: To systematically introduce the design of case-cohort study and the statistical methods of relative risk estimation and their application in the design. Methods: First, we introduced the basic principles of case-cohort study design. Secondly, Prentice's method, Self-Prentice method and Barlow method were described in the weighted Cox proportional hazard regression models in detail, finally, the data from the Shanghai Women's Health Study were used as an example to analyze the association between obesity and liver cancer incidence in the full cohort and case-cohort sample, and the results of parameters from each method were compared. Results: Significant association was observed between obesity and risk for liver cancer incidence in women in both the full cohort and the case-cohort sample. In the Cox proportional hazard regression model, the partial regression coefficients of the full cohort and the case-cohort sample fluctuated with the adjustment of confounding factors, but the hazard ratio estimates of them were close. There was a difference in the standard error of the partial regression coefficient between the full cohort and the case-cohort sample. The standard error of the partial regression coefficient of the case-cohort sample was larger than that of the full cohort, resulting in a wider 95% confidence interval of the relative risk. In the weighted Cox proportional hazard regression model, the standard error of the partial regression coefficient of Prentice's method was closer to the parameter estimates from full cohort than Self-Prentice method and Barlow method, and the 95% confidence interval of hazard ratio was closer to that of the full cohort. Conclusions: Case-cohort design could yield parameter results closer to the full cohort by collecting and analyzing data from sub-cohort members and patients with the disease, and reduce sample size and improve research efficiency. The results suggested that Prentice's method would be preferred in case-cohort design.
Subject(s)
Female , Humans , China/epidemiology , Cohort Studies , Proportional Hazards Models , Risk , Sample SizeABSTRACT
Cancer causes a considerable disease burden in countries all over the world. Numerous epidemiological evidences suggest that dietary antioxidants are closely related to the incidence， mortality and prognosis of cancer. For example， many antioxidants in fresh vegetables， fruits and legumes have beneficial effects in preventing some common cancers and improving patient survival. Based on our relevant research experience and reported studies from home and abroad， this paper summarizes the results of various epidemiological studies on the association between dietary antioxidants and cancer. Healthy diet education should be conducted in general population for cancer prevention and control.
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Objective: To investigate condom use among unmarried female migrant workers in Shanghai and explore its relation with some psychosocial problems. Methods: A questionnaire survey was conducted by cluster random sampling. A total of 903 unmarried female migrant workers who had sexual experience were enrolled to evaluate their condom use and psychosocial factors. Logistic regression was used to analyze the related factors of condom use. Results: Among the unmarried female migrant workers, the percentage of consistent condom use was only 13.8%. Univariate Logistic regression showed that low self-esteem (OR=0.47, 95% CI=0.25-0.90) and depression (OR=0.59, 95% CI=0.38-0.93) were related to inconsistent condom use after correcting demographic factors. Multivariate Logistic regression showed that depression (OR=0.58, 95% CI=0.37-0.90) was the main factor related to inconsistent condom use. The participants with at least two psychosocial problems were more difficult to use condoms consistently (OR=0.56, 95% CI=0.32-0.97). Conclusion: The unmarried female migrant workers with depression or co-occurring psychological problems in Shanghai are more likely to have unsafe sex behavior, which indicates the importance of psychological interventions.
ABSTRACT
Objective·To compile the osteoporosis prevention and control behavior scale for health care workers in community and evaluate its validity and reliability.Methods·In 20 standardized diagnosis and treatment pilot community health service centers for osteoporosis in Shanghai,400 health care workers were conveniently sampled to conduct the survey and 20 of them who were randomly sampled underwent retest 2 weeks later.The validity of the scale was evaluated by content validity and structural validity.The reliability of the scale was tested by Cronbach's αt coefficient,retest reliability and split-half reliability.Results·A total of 19 items were retained after project analysis.Scale-level content validity index/universal agreement (S-CVUUA)and scale-level CVI/average (S-CVI/Ave) were 0.944 and 0.992,respectively,after an entry with item-level CVI (I-CVI) less than 0.78 was deleted.Four common factors were extracted by exploratory factor analysis,and the cumulative variance contribution rate was 85.94％.Results of confirmatory factor analysis indicated that the model was consistent with the theoretical assumption,and the fitness indexes x2/df,CFI,GFI,and RMSEA were 3.323,0.971,0.902,and 0.076,respectively.The overall Cronbach's α coefficient of this scale was 0.978 and the Cronbach's αt coefficients of the four dimensions were all over 0.9.The intraclass correlation coefficient (ICC) of each item was greater than 0.7,and the ICC of the total scale was 0.654.The split-half reliability coefficient was 0.932.Conclusion·The osteoporosis prevention and control behavior scale has good reliability and validity and can be used to evaluate the implementation of osteoporosis prevention and control behavior of health care workers in community.