The player character has primary stats, skills and perks - all numerical values which determine actions' chances of success according to mathematical formulas, as well as derived statistics such as hit points. Beginning stats are chosen during a series of tutorial quests and may be changed just before exiting Vault 101. Experience Points are awarded for successful completion of actions. Acquiring enough experience points causes the player character to level up, upon which skill points are distributed by the player and an additional perk chosen.