Let say you have an 101 Defense. You use Eviolite. The boost given will be 50.5, resulting in a 151.5 Def stat. Will it be rounded up to be 152, or will it be rounded down to 151?
Same with stat boosts.
If you don't know, most things in pokemon are rounded down and this isn't a exception. So with the boost, you would have 151 Defense.
Source: Tested on PO and experience with rounding mechanics.