NeighborhoodScout uses a population figure based on the 2010 Census because each decennial census does a complete census of population for each neighborhood (census tract).  More recent data from the census is from the American Community Survey, which is based on a sampling of people and thus is less reliable for small areas like census tracts, though the sampling works fine for entire cities and counties which are larger and thus have larger samples.  

We choose to work with the more reliable complete figure.