We present a spectroscopic sample of 910 distant halo stars from the Hypervelocity Star survey from which we derive the velocity dispersion profile of the Milky Way halo .
The sample is a mix of 74 % evolved horizontal branch stars and 26 % blue stragglers .
We estimate distances to the stars using observed colors , metallicities , and stellar evolution tracks .
Our sample contains twice as many objects with R > 50 kpc as previous surveys .
We compute the velocity dispersion profile in two ways : with a parametric method based on a Milky Way potential model , and with a non-parametric method based on the caustic technique originally developed to measure galaxy cluster mass profiles .
The resulting velocity dispersion profiles are remarkably consistent with those found by two independent surveys based on other stellar populations : the Milky Way halo exhibits a mean decline in radial velocity dispersion of -0.38 \pm 0.12 km s ^ { -1 } kpc ^ { -1 } over 15 < R < 75 kpc .
This measurement is a useful basis for calculating the total mass and mass distribution of the Milky Way halo .