Аннотация:Zhang et al. (Feb. 27 issue) 1 present data confirming the finding of the Study of Osteoporotic Fractures Research Group 2 that increased bone mass in postmenopausal women is associated with an increased risk of subsequent breast cancer.However, I am concerned about the accuracy of the multivariate-adjusted rate ratios that Zhang et al. report.The authors included 10 variables in addition to bone mass in their multivariate model.Since the number of observed events (i.e., cases of breast cancer) was only 91, the ratio of the number of events to the number of variables is less than 10.As a rule of thumb, this ratio should be at least 10 in order to prevent overfitting. 3Models that are overfitted may give results that are numerically unstable and too dependent on the observed data. 4This may be evidenced by overly large coefficients or standard errors.Can the authors allay this concern by indicating the estimated coefficients and standard errors or perhaps by repeating the analysis after omitting some of the less important variables?In addition, perhaps the authors could indicate whether they checked their model for goodness of fit and for conformity to the assumption of proportional hazards.
