Just to further emphasize RDan's point, I would say that while the base shield bonus is nice, it quite soon starts to pale in comparison to Dodge's ability to apply to multiple attacks from all directions with no prerequisites (such as holding a specific physical object in the hand) and no skill checks.
A low level character trying to use a Normal shield does get a +20 bonus over a character trying to Dodge, but that Shield only applies to the frontal arc and only to a maximum of two attacks, and the character even needs to make a check to apply the bonus to the second attack.
Compare to the Dodger. The Dodger already gets at least one rank (possibly 2) in Dodging from Culture, which starts to close the gap created by the base shield DB bonus. The bonus she gets applies to all directions, and an infinite number of attacks. That alone often gives the advantage to the Dodger.
And then as you rank up in levels, the discrepancy really starts to favor the Dodger. At 10 ranks, would you rather have a +70 Shield bonus that requires you to have a hand free, to be carrying a physical shield, and further only applies to a maximum of two attacks, which must be through your frontal Arc? Or would you rather have a +53 or +56 Dodge bonus that does not require you to have a free hand or physical shield, and which applies to an infinite number of attacks, even rear attacks?
Now ask the question again at 20 ranks, where the question is a very conditional +100 bonus vs a maximum of 2 attacks or a very unconditional +82 or +84 bonus that applies infinitely and in all directions? The choice is pretty clear... and especially so if you are the party tank who often has to face off against multple enemies, many of whom can multiattack.
I do see a significant disrepancy there, and there is also the further issue of divergent mechanics. I would prefer if active blocking, whether via Shield or Dodge, worked according to the same mechanic: to get an active bonus, you need to see the attack coming and be able to block or dodge it.