There was not significant interaction between the family history and the first delivery at the age of 35 yrs and more or no delivery. However, our study show that the sample size of 300 subjects to investigate

interaction in case control studies is not enough, and that case-only BI 6727 designs might be a better design to examine such an interaction in such a sample size. The independence assumption of the two factors was not established in a study by Ardalan and colleagues,12 Inhibitors,research,lifescience,medical and therefore was removed from the case-only analysis. In agreement with the findings of Yavari et al.4 the present study showed that case-only design had more efficiency than that of the matched case-control designs. The interaction of family history of breast cancer and the history of having live birth was not statistically significant in the case-control design. Since the Inhibitors,research,lifescience,medical independence assumption was not established, the interaction of these two factors in case-only design was

not estimated in the study by Yavari and colleagues,4 or was not reported in Becher et al. studies.11 The present study showed that the confidence interval, standard error and -2log likelihood estimations Inhibitors,research,lifescience,medical in case-only design were smaller than those in case-control analogues. These findings are similar to that of Ardalan and colleagues,12 and is an indication of more efficacy of case-only designs than the case-control ones. The confidence interval, standard error, -2log likelihood and p-value estimations in case-only design were smaller than those in the case-control design. This shows that the case-only design had more efficacy than the case-control one. The confidence interval, standard Inhibitors,research,lifescience,medical error, and -2log likelihood estimations in the case-only design were smaller than those in the case-control design. Such findings are a sign that case-only designs are more efficacious than the case-control design. However, the P value in the case-only design was higher than that

in the case-control design. The reason for not detecting the interaction between the family history of breast cancer and other variables might be the Inhibitors,research,lifescience,medical small sample size of the participants in case-control design study. In case-only studies, the basic assumption of gene-environment independence in non-diseased group should be established. In the studies before 2004, this assumption used to be established DNA ligase using classic statistical tests such as Chi Square, Correlation Coefficient and so on. However, such an approach was also criticized,25 for the lack of ability of the use of GE-OR in control groups to estimate the GE-Or in populations. Gatto et al.17described a modification of the methods. In order to establish the independence assumption, they introduce the standard statistical multivariable techniques, which have resolved the previous shortcoming of the design, and have led to widespread use of the techniques. The studies of Yavari et al.4 and Becher et al.