Effort values

Effort values (abbreviated EVs and previously called Stat XP) are attributes which give bonuses to a Pokémon's stats and improve differently depending which Pokémon they defeat. These bonuses are gained in addition to bonuses gained by increasing level. A Pokémon which increases in level using a Rare Candy instead of battling does not gain any EVs, making it weaker than a Pokémon who increases in level normally.

Roughly speaking, defeating fast Pokémon increases Speed better than fighting slow Pokémon, defeating Pokémon with high hit points improves HP more than defeating Pokémon with low HP, and so on. For example, fighting 100 Machop will improve a Pokémon's attack stat more than fighting 100 Abra of the same level, whereas the Abra will improve the Special Attack stat more. For a list of the effort points that Pokémon give away on their defeat, see list of Pokémon by effort value yield.

Overview

Generation I

In Generation I, the basic EV system was introduced, called stat experience, or Stat Exp. A Pokémon could have a maximum of 65536 Stat Exp points in every stat. A Pokémon defeated in battle would give out Stat Exp equal to its Base Stats (for example, battling a Mew would give 100 Stat Exp points in every stat).

Vitamins would give 2560 Stat Exp in a stat, and would have no effect if that stat already had at least 25600 Stat Exp.

A Pokémon's stats will be a certain number of points higher in a specific stat corresponding to the amount of Stat Exp gained in that stat compared to an untrained counterpart. Though leveling up stops at 100, addition of Stat Exp can continue indefinitely, until the Pokémon reaches the maximum possible value for their stats using the box trick, where a Pokémon's stats are recalculated to reflect the amount of Stat Exp it has gained when it is deposited in a PC.

At level 100, the formula for determining the stat difference between a Pokémon trained in that stat and an untrained Pokémon is File:Statexp.png

Generation II

In Generation II, the basic structure did not change much, excepting the fact that now, instead of having five stats, there were six. Both Special Attack and Special Defense were calculated using the effort points for Special, causing both to rise by the same amount for each and every Pokémon. Like in Generation I, the box trick could be performed.

The Pokérus virus, a rare status condition, was also introduced. It would double the amount of effort points gained in battle.

Generation III

In Generation III, the effort value structure, like many other things, was overhauled completely. Each Pokémon would give out either 1, 2, or 3 effort points, depending on its species, in a particular stat (Attack, Defense, Speed, Special, or HP). With these effort points, a Pokémon would get stronger in a specific stat by battling the same kind of Pokémon over and over. For example, continually battling Jolteon after Jolteon, with its high speed, would cause a Pokémon to eventually have a higher Speed. At level 100, a Pokémon's stats will be one point higher in a specific stat for every four effort points gained in that stat compared to an untrained counterpart.

A Pokémon now could not have an effectively infinite amount of training, but was limited to 510 effort points total, with 255 effort points being the maximum for an individual stat. This means that two stats could be maxed out (with 252 being the highest number evenly divisible by four), while another stat could get one more point. The box trick could still be performed, but only on Pokémon up to level 99. Level 100 Pokémon were unable to receive any effort values from battling no matter what.

The vitamins of the previous two generations would instead add 10 effort points to a specific stat, and could not be used if the specific stat was at or above 100 effort points, or the total effort points amounted to 510 or more. Likewise, the Special Attack and Special Defense stats were finally split, and Zinc was introduced so as to give the Special Defense stat a vitamin enhancement.

A held item, the Macho Brace, was also introduced; it would double the amount of effort points gained in battle, providing for faster training. Utilized with the Pokérus, which makes a return, it provides four times the amount of effort points per Pokémon.

Also, in Pokémon Emerald, certain Berries that were previously only used to make Pokéblocks were now able to decrease a certain effort value by 10, while increasing the happiness of the Pokémon they were used on.

Generation IV

In Generation IV, while not much changed from Generation III, due mostly to the data structure remaining much the same, a series of items were introduced that would automatically add four effort points per Pokémon battled in a specific stat.

Stat	Item
HP		Power Weight
Attack		Power Bracer
Defense		Power Belt
Special Attack		Power Lens
Special Defense		Power Band
Speed		Power Anklet

They would, however, also add whatever the Pokémon defeated would naturally add. For example, a Pokémon defeating a Bidoof while holding the Power Lens would get 4 Special Attack effort points, as well as the 1 HP effort point Bidoof naturally rewards; defeating a Bidoof while holding the Power Weight would yield 5 HP effort points. The total yields are also doubled by Pokérus: defeating a wild Pineco would yield 2 Defense and 8 Special Defense when the player's Pokémon is holding a Power Band and has the virus.