That chart claims to be showing "expected returns for 1/1/1979 - 12/31/2015" for "the Dow Jones U.S. Total Stock Market Index," am I right?
And yet, at
the index provider's website, in the factsheet, we learn that the launch date and the first value date of the Dow Jones U.S. Total Stock Market Index" was January 1st, 1987.
So... there is something
wrong there. Sloppiness, probably, but something
wrong, because they are showing statistics for the period 1979-2015 inclusive,
for an index that didn't exist until 1987.
This should at least convince you to take this stuff with a grain of salt. It's not my job to explain what they might or might not have done, but my guess is that they are playing fantasy football--calculating something over a shorter period of time, then extrapolating that over a longer period of time.
But it gets worse, because they claim to be showing you, again, 1979-2015 values for the "Dimensional US Small Cap Value index." But, as the fund literature always says, you can't invest directly in an index, only in an actual fund--and the DFA US Small Cap Value Portfolio
Fund only began in 1993:
So this chart is including performance for periods of time when the indexes shown didn't exist--and then even when they did exist there was no way to invest in them because the funds that track them didn't exist.
Annual income twenty pounds, annual expenditure nineteen nineteen and six, result happiness; Annual income twenty pounds, annual expenditure twenty pounds ought and six, result misery.