One problem with any studies that involve very long intervals of DJIA values, is that the DJIA is probably not the best long term representation of stock market value. That's been discussed in many articles. Here is a portion of one:

"...Perhaps the most celebrated illustration of the Dow’s failure to represent the overall market traces back to a 1939 decision to delete International Business Machines from the Dow 30 list. I.B.M. wasn’t restored to the index until 1979. Norman Fosback, editor of Fosback’s Fund Forecaster newsletter, has estimated that the Dow would have been more than twice as high in 1979 had I.B.M. stayed in the index continuously...."

That's from this Mark Hulbert article, which also deals with distortion introduced by deflation and dividends.