How do followers' attributes increase from item bonuses?

Solution 1:

Followers gain a 2.5x multiplier to base stats on items (Str, Dex, Int, Vitality). This is because they are only able to equip jewelry and weapons - in order for their stats to remain competitive with more difficult monsters, they need the boost. In addition, they contribute to the hero's Magic and Gold Find, as well as Bonus XP, but only at a 0.2 multiplier - so, if your follower doesn't need the additional power, you can use them as a way to stack some extra +loot items and benefit that way.

Other item stats, such as +damage and on-hit effects work as normal.