The conditional mean spectrum (CMS) has been recently proposed as an alternative to the uniform hazard spectrum (UHS) to be employed as a target spectrum in ground motion record selection. The CMS provides the expected response spectrum, conditioned on occurrence of a target spectral acceleration value at the period of interest. A robust regression analysis is proposed in this manuscript to improve the current CMS which is based on a conventional regression analysis. The results show that the proposed robust CMS significantly differs from the conventional CMS, especially for higher periods of interest. The shape of the robust CMS represents the rare ground motions in a more reliable manner, comparing with the conventional CMS.
