The SLS^TM model fit comprehensive child-growth data better and more efficiently than any method,
typically spline-regression.  
Hence, SLS^TM enabled integration of race-specific growth patterns with the WHO pediatrics DB that covered all ages but was non-specific for race.
Subsequently, a year or so later, the WHO also upgraded their DB to include the impact of race.
REF:L Comanor, J M Minor, et al, 2001, Impact of chronic hepatitis B and interferon-a therapy on growth of children, J. Viral Hepatitis 8, 139-147