  Observables such as the luminosity function of galaxies, \Phi(M), the
projected clustering of galaxies, w_p(r_p), and the galaxy-galaxy lensing
signal, \Delta\Sigma, are often measured from galaxy redshift surveys assuming
a fiducial cosmological model for calculating distances to and between
galaxies. There is a growing number of studies that perform joint analyses of
these measurements and constrain cosmological parameters. We quantify the
amount by which such measurements systematically vary as the fiducial cosmology
used for the measurements is changed, and show that these effects can be
significant at high redshifts (z~0.5). We present a simple way that maps the
measurements made using a particular fiducial cosmological model to any other
cosmological model. Cosmological constraints (or halo occupation distribution
constraints) that use the luminosity function, clustering measurements and
galaxy-galaxy lensing signal but ignore these systematic effects may
underestimate the confidence intervals on the inferred parameters.
