How does the Bolster effect in Warzones work?

Solution 1:

Pre-release the best formula thrown around was roughly described as follows:

If you are ‘naked’ in a bracketed match then you will be up to a 90% combat stats disadvantage. If you are in an open match then the bolster mitigates the difference, not the whole. In other words, you will be at about a ((your level/max level) * 80%) + 10% combat stats disadvantage. Note that formula is an oversimplification for illustrative purposes.

Link for this is here: http://www.swtor-life.com/humor/under-the-hood-the-forumulas-behind-the-mayhem/2268/

I would imagine the actual formula is much more complex to take gear into account, however, practice seems to show that "twinked" 50s gear allows a huge advantage, so, the formula, when it comes to light, is not one for the mind-bending math junkies.

Solution 2:

Bolster has changed dramatically in Game Update 2.0. Now:

• Your base stats are scaled based on your level, to essentially make you a Level 50 and compensate for any skills you may be lacking. This was true of the previous Bolster but was much less nuanced.
• Your gear is scaled to an "expected" Level 50 value.

Unfortunately, it is quite difficult to produce anything resembling real numbers because you'd have to test in a huge variety of gear against various opponents in a huge variety of gear, and then repeat for every level combination! However, there is also no need for numbers. You will see a small boost at higher levels due to better skills and the ability to develop a proper rotation and manage your resources (which is why the lowbie PvP brackets are now 1-29 and 30-54) but the intent is for that effect to be minimal, with the real difference coming from personal skill and the Expertise stat.

Expertise has also been completely re-worked. It now has no diminishing returns and is completely linear (your last point is as helpful as the first). All endgame PvP gear has the same amount of Expertise and only differs in the amount of other stats. As noted at the link in my first bullet above:

Once you get your full set of PvP gear you will have the max of your ‘PvP stat’. Later sets will have more primary, secondary and tertiary stats and increasing these stats will be how PvPers gain power in PvP, rather than going after a pure PvP stat.