9. Diminishing Returns
Diminishing Returns on avoidance stats were introduced in Wrath of the Lich King to stop tanks reaching 100% avoidance against bosses (druids and rogues could literally not be hit by a boss). Both parry and dodge ratings diminish at the same rate. As they decay at the same rate, and start at the same point, one should try to balance the ratings.
This is a very simplified example of how Diminishing Returns works (in reality the maths and numbers are rather more complex):
Assuming 1 dodge rating is 1% dodge and that the next rating point grants 0.01% dodge less each time, diminishing returns works a bit like this:
The first point of dodge rating gives 1% dodge.
The next 1 dodge rating gives 0.99% dodge (2 dodge rating = 1.99% instead of 2%)
The next 1 dodge rating gives 0.98% dodge (3 dodge rating = 2.97% instead of 3%)
The next 1 dodge rating gives 0.97% dodge (4 dodge rating = 3.94% instead of 4%)
The next 1 dodge rating gives 0.96% dodge (5 dodge rating = 4.90% instead of 5%)
Now I said to balance the ratings because of the diminishing return. This is the reason why:
5 Parry Rating = 4.90%
3 Dodge Rating = 2.97%
Total = 7.87% Avoidance
Now if the ratings were balanced... (note we still have the exact same number of points)
4 Parry Rating = 3.94%
4 Dodge Rating = 3.94%
Total = 7.88% Avoidance
7.88% > 7.87%
By shifting one parry rating into dodge rating, our avoidance has increased by 0.01%, even though the total amount of rating remained constant.