Addressing Complete Separation in Male Infertility Risk Factor Modeling: A Firth Logistic Regression of BMI and Vitamin E

Background

About 7% of men are affected by male infertility, up to 50% of cases remaining idiopathic. Proposed risk factors such as elevated BMI and reduced vitamin E show inconsistent evidence. Standard logistic regression often fails against Quasi-complete separation, a common statistical issue in case-control studies, and no data exist from Iraqi populations.