This study investigates the variation in stiffness modulus values of bituminous concrete with the fractional change in percentage mixing of styrene–butadiene–styrene (SBS) polymer. The study is done through the application of two-tailed hypothesis testing. The objective of this study is to determine if there is a significant mean difference in the stiffness modulus of bituminous concrete when different proportions of SBS are added. The research aims to determine the ideal proportion of SBS that maximizes bituminous concrete performance. The present analysis involves preparing bituminous concrete samples with varying SBS content, conducting standardized tests, and applying statistical methods to assess the significance of observed mean differences. The results indicate a mixing proportion percentage to arrive at the optimal range for SBS content, providing a robust basis for enhancing bituminous concrete formulations.