In the

present study, such an assumption was investigated using standard statistical multivariable techniques.17 In the equation, G-EORinD-1 represents the OR of gene-environment in the control group and the G-EORinPop represents the OR of gene-environment in the population. If C/PROR is equal to one, the control group can be used to estimate the OR of interaction of genetic and environmental factors in the population. In the above equation, P (D/G-E-) represents the disease baseline risks, which shows the likelihood of disease occurrence in people, who do not have the gene and environment factors. The RRGE or ORGE represents the OR of the Inhibitors,research,lifescience,medical disease in those who have both, the gene and the environmental factors (ie, two-factor interactions). The RRG or ORG represents the OR of the disease in people who have only the gene factor and RRE or ORE represents the OR of the disease in people who have only the environmental Inhibitors,research,lifescience,medical factor.17 The case-control and case-only designs were compared in terms variations in standard error,

-2Log likelihood, and 95% confidence interval for of the gene-environment interactions.5 Statistical analyses were performed Inhibitors,research,lifescience,medical using STATA 8.0 statistical software. The measured independent variables included continuous use of oral contraceptives for the past five years, breastfeeding history, number of pregnancies, age at menarche, age at the first delivery, and the history of breast cancer in the family. The family history of breast cancer in the first degree relatives including mother or sister was used as a proxy for the disease I-BET151 molecular weight susceptibility.11 Conditional Logistic Regression

was used Inhibitors,research,lifescience,medical for data analysis of matched case-control design. Results The age of the case group was 51.8±0.5 years. The OR of interaction between family history of breast cancer in the first degree relatives and other variables such as the first delivery at the age of 35 years and more, or no delivery, the history of having live birth, breastfeeding history, and oral Inhibitors,research,lifescience,medical contraception use were not statistically significant. Assessing Independency Assumption and Case-Only Study The findings regarding the independency assumption of gene-environment are shown in table 1. There was independence between the gene-environment Mephenoxalone factors in the control group, therefore, in the second step we could use interaction analysis using case-only study for all variables. Table 1: The ratio of control to population odds ratio for the relation of family history to other variables of the participants The findings of assessment of GE-OR in the control group as a surrogate of GEOR in the population are shown in table 1. All control/population ratio of odds ratio were approximately close to 1. The Efficiency Comparison of Case-Control and Case-Only Designs Odds ratio for GE interaction and the comparison of efficiency of case-control and case-only design are shown in table 2.