How much does a Choice item increase it's dedicated stat?

Question

This applies to each of the Choice items (Scarf, Band, Specs). When I give a Choice item to my Pokémon, how much does it increase the stat it applies to?

For example:

At level 50, a Jolly natured, 252 EV, 31 IV Tyranitar reaches 124 Speed. Once I add on the Choice Scarf, how much does it increase the Speed by?

EDIT: And does the boost given by a Choice item measure the same as a regular stat boost? For example, if I was at +1 Attack, would the boost be the same as that of a Choice Band?

Answer 1

It increases it by 1.5 times, or by 50%. For example, if your Tyranitar is at 124 speed, the Choice Scarf will increase it by 1.5x, which is 186 speed. (124*1.5)

Yes, if you are for example, at +1 Speed for Tyranitar, the effective speed is the same as when holding a Choice Scarf.