Are the Luminosities of RR Lyrae Stars Affected by Second Parameter Effects?

There is a serious discrepancy between the distance to the LMC derived fromthe Cepheid Period-Luminosity relation and that obtained by using the Galacticcalibration for the luminosity of RR Lyrae stars. It is suggested that thisproblem might be due to the fact that second parameter effects make itinappropriate to apply Galactic calibrations to RR Lyrae variables in theMagellanic Clouds, i.e. Mv(RR) could depend on both [Fe/H] and on one or moresecond parameters.