Stats
Pokemon Mystery Dungeon Origins uses all 6 stats from the main series games.
Basic Information
HP, Attack, Defense, Special Attack, Special Defense all behave as they do in the main series. The damage formula is based on division.
Speed determines hit rate and dodge rate: When attacking a target, the accuracy of the move is multiplied by your speed, then divided by the target's speed to get the final percentage hit chance. Remember that no attack can miss twice in a row.
Stat Calculation
Pokemon base stats are based on main series stats from ORAS.
Boosting Stats
Gummis and Vitamins can boost stats permanently.
Stat Modifiers
Stat modifiers have 6 stages. They can be boosted up to +6, or dropped to -6. The sole exception is Movement Speed, which can be boosted to +3, or dropped to -3.
Stat modifiers that are not Movement Speed modify the Pokemon's stats using a numerator/denominator of 3: