In particular, in the earlier parts of the series, Theck discerned the new formula for working out each avoidance stat after diminishing returns. As a result, he was able to plot out (for plate tanks in particular) the proper ratio that dodge and parry should be balanced at.
Right now, on live, we want to keep parry and dodge as absolutely close as possible. The two have the same diminishing returns curve, which means that x points of parry will be diminished exactly the same as x points of dodge. As such, if you have 3% more parry than dodge, you're losing a non-zero amount of avoidance to the gaping maw of diminishing returns that you might otherwise keep if it was reforged to dodge.
However, as Theck has discovered, the DR curves were bent significantly apart in Mists, to the point that we'll want much more parry to keep an even ratio with dodge -- about three times more parry, to be exact.