The quote below is from John Bogle (former Chairman of Vanguard Investments)

The most fundamental decision of investing is the allocation of your assets: How much should you own in stock? How much in bonds? How much in cash reserves? . . . That decision [has been shown to account] for an astonishing 94% of the differences in total returns achieved by institutionally managed pension funds. . . There is no reason to believe that the same relationship does not also hold true for individual investors. John Bogle

Mr. Bogle emphasizes the importance of asset allocation and indirectly cites the results of the Brinson study as proof. However, there is an error in Mr. Bogles quote.

I need help to identify and explain the error.