Probably most consequential: The index is now computed with a geometric mean, instead of an arithmetic mean
A geometric mean is also used to build up the overall education index from its two components
Traditional HDI added the three components and divided by 3
New HDI takes the cube root of the product of the three component indexes
The traditional HDI calculation assumed one component traded off against another as perfect substitutes, a strong assumption
The reformulation now allows for imperfect substitutability