Effort values (abbreviated
EVs and previously called
Stat Exp), officially called
base stats (Japanese:
きそポイント base point), are attributes which give bonuses to a Pokémon's stats and improve differently depending which Pokémon they defeat. These bonuses, in the form of effort points, 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.
Unlike experience points, which are reduced when multiple Pokémon are receiving experience, effort points are awarded equally to all Pokémon who participated in defeating a Pokémon. Though they are shared, each of the Pokémon will receive the standard amount of effort points.
In Generation I and Generation II effort points given are equal to the Pokémon's base stats. For a list of the effort points that Pokémon give away on their defeat in Generation III, Generation IV, and Generation V see list of Pokémon by effort value yield.
Gaining effort points to increase desired EVs varies from being simple to complicated, depending on whether one wants their Pokémon to fully max out its stats or raise them to balanced heights. Should a Pokémon attain the maximum amount of 510 effort values, it will be eligible to receive an Effort Ribbon to signify this achievement (Generation III and IV). In Pokémon Black and White, there is an NPC in a house in Opelucid City who will tell the player if the Pokémon at the front of his or her party has attained 510 total effort values. In Pokémon Black 2 and White 2, Bianca, when called on the Xtransceiver, will tell the player whether a certain Pokémon in the party has attained 510 total effort values. She will also notify the player if a Pokémon has reached 252 effort values in any stat.
Effort values only appear in the main series Pokémon games, and are not present in the spin-off games, such as the Mystery Dungeon series.
Individual values,
IVs for short, sometimes also known as
determinant values,
DVs for short, are the Pokémon equivalent of genes. They are instrumental in determining the stats of a Pokémon, being responsible for the large variation in stats among untrained Pokémon of the same species.
In Generation III, the IV system was completely overhauled. Now, rather than having a range of 0-15, IVs would have a range of 0-31, with HP and Special Defense getting their own individually-determined IVs. The formula for calculation of stats by IVs was also changed, as with the IV system the EV system was also modified, and Natures, newly-introduced, now modified certain stats either by raising or lowering them by 10%. The personality value handles a Pokémon's gender, Shiny status, and several other aspects.
This new system is part of the reason why it is impossible to trade between Generation II and Generation III games.
The Generation III-on determination of stats follows the following two formulas:
The IVs are now all stored together as a single 32-bit integer, separate from the equally-large personality value, which is used to determine other aspects of a Pokémon. This integer's highest bits, single numbers, determine which of two Abilities a Pokémon has (if it has potential to have more than one) and whether or not the Pokémon is an unhatched egg or not. The remaining 30 bits are the IVs, five bits apiece, in the order of Sp. Def, Sp. Atk, Speed, Defense, Attack, and HP.
For two Marill caught on Route 120: