Effort values (努力値 doryokuchi ), often abbreviated to EVs, are hidden values in the main Pokémon series of video games that affect the strengths of a Pokémon in particular statistical areas. Differing effort value levels between two Pokémon can create a significant difference in the two Pokémon's statistical strengths. When a Pokémon battles and defeats an opponent, they gain experience points and also receive a number and type of EVs according to the defeated Pokémon's species. Every defeated Pokémon gives at least one EV to each of the Pokémon that fought it. Certain factors, such as holding the Macho Brace, can increase the rate at which EVs are gained in battle. In Pokémon Gold and Silver Versions, a condition known as Pokérus was introduced which doubles the rate at which EVs are obtained, and will be contagious for a certain number of days, allowing it to spread to other Pokémon. Also, consuming certain items can increase a Pokémon's EVs, and certain Berries decrease EVs while increasing a Pokémon's friendship value. There is a limit on the number of EVs Pokémon can have, which prevents stats from increasing indefinitely. The total limit allows for maximum effort values in two stats simultaneously.
In the Generation I and Generation II games, a similar system usually referred to as Stat Experience or Stat Exp. was used. As with effort values, there is a limit to how much Stat Exp. a Pokémon can have in each stat; however, unlike Effort Values, there is no limit to the total Stat Exp. a Pokémon can have across all stats, meaning that a Pokémon can have maximum Stat Exp. in every stat. Also of note is that, for Pokémon from the first and second generation to be forward and backward compatible for trading, Stat Exp. was not tracked separately for Special Attack and Special Defense in the Generation II games. Instead, the Special Stat Exp. value was used to calculate both Special Attack and Special Defense.
In Pokémon X and Y, a minigame known as Super Training is introduced that allows players to more accurately manage the effort values. The player can do this by playing a soccer-like minigame, which also rewards the player with training bags to continue the training passively. The Pokémon's effort values can also be viewed in the Super Training interface, which includes an Effort-o-Meter to allow the player to see the maximum capability of increasing the Pokémon's effort values.
In Pokémon Sun and Moon, a graph of a Pokémon's EVs along with its base stats can be seen by pressing the Y button while viewing the summary of a Pokémon. A sparkling stat shows that the Pokémon had obtained the maximum number of EVs for the stat. Pokémon can gain EVs passively through a feature called Poké Pelago.