Hammurabi Journal of Medical Sciences
Addressing Complete Separation in Male Infertility Risk Factor Modeling: A Firth Logistic Regression of BMI and Vitamin E
By Noor Kamil Hussein Al-Mayahy and Mohammed Talib Al-Tameemi.
Abstract
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.
Objective
To assess the independent associations of BMI and serum vitamin E with idiopathic male infertility using Firth's penalised logistic regression to overcome separation. Materials and Methods: This case control study included 160 men (80 infertile men, 80 controls) from Najaf, Iraq. BMI was recorded, and serum vitamin E was measured by a validated colorimetric assay. Firth's logistic regression was applied.