We have compiled a sample of 699 stars from the recent literature with detailed chemical abundance information ( spanning -4.2 \lesssim [ Fe/H ] \lesssim + 0.3 ) , and we compute their space velocities and Galactic orbital parameters .
We identify members of the inner and outer stellar halo populations in our sample based only on their kinematic properties and then compare the abundance ratios of these populations as a function of [ Fe/H ] .
In the metallicity range where the two populations overlap ( -2.5 \lesssim [ Fe/H ] \lesssim - 1.5 ) , the mean [ Mg/Fe ] of the outer halo is lower than the inner halo by \sim 0.1 dex .
For [ Ni/Fe ] and [ Ba/Fe ] , the star-to-star abundance scatter of the inner halo is consistently smaller than in the outer halo .
The [ Na/Fe ] , [ Y/Fe ] , [ Ca/Fe ] , and [ Ti/Fe ] ratios of both populations show similar means and levels of scatter .
Our inner halo population is chemically homogeneous , suggesting that a significant fraction of the Milky Way stellar halo originated from a well-mixed ISM .
In contrast , our outer halo population is chemically diverse , suggesting that another significant fraction of the Milky Way stellar halo formed in remote regions where chemical enrichment was dominated by local supernova events .
We find no abundance trends with maximum radial distance from the Galactic center or maximum vertical distance from the Galactic disk .
We also find no common kinematic signature for groups of metal-poor stars with peculiar abundance patters , such as the \alpha -poor stars or stars showing unique neutron-capture enrichment patterns .
Several stars and dSph systems with unique abundance patterns spend the majority of their time in the distant regions of the Milky Way stellar halo , suggesting that the true outer halo of the Galaxy may have little resemblance to the local stellar halo .