What is a reward schedule?
A reward schedule is the reinforcement timings in which to reward the player in the game for accomplishing a certain action. There are 4 base types of reward schedules: Fixed Ratio, Variable Ratio, Fixed Interval, and Variable Interval.
In a fixed ratio reward schedule, the player is rewarded for completing an action a set number of times. The number is pre-determined, so the player can calculate exactly how many more times the action needs to be achieved before they are rewarded again. (Example: In Tetris, the player is rewarded every time they clear a line of horizontal blocks.)
In a variable ratio reward schedule, the player is reward for completing an action in a random, or semi-random, amount of times.
(Tetris Example: You are given another block if you do not lose while placing the previous block.)
(Example: In World of Warcraft, when a player kills a mob character the player has a random chance in receiving an item.)
In a fixed interval ratio reward schedule, the player is rewarded for completing the action within a pre-determined amount of time. It is important to note that it does not matter if the player has completed the action 1 time or 100 times, they only receive the reward once per interval.
(World of Warcraft Example: Players receive “rested exp” as a bonus experience for putting the game down. Although it may seem counter intuitive, all players do stop playing after a certain session. The reward is for logging back on and capitalizing on the bonus experience before it reached the maximum stored capacity)
(Example: In League of Legends, the player is rewarded bonus in-game currency once every 24 hours for winning a game session)
In a variable interval reward schedule, the player is rewarded for completing the action in a random, or semi-random, amount of time. Like fixed interval reward schedules, it does not matter how many times the player has completed that action within the given time interval, it only matters if the player has completed the action at least once. (Example: I actually cannot think of one implemented effectively, which will be explained below.)
Which scenarios are best for each type of reward schedule?
Fixed ratio reward schedules provide the player with a sense of reliability, every time the player performs the action, they will expect the same outcome and therefore are most commonly used for the most common or minor actions in a game, such a killing a mob for experience or receiving damage after falling from a certain height.
Variable ratio reward schedules are a strong reinforcement effect than fixed ratio and are meant to habituate the player to continually complete a certain action within the game in hopes of getting the reward again. This is most commonly seen in Massively Multiplayer Role Playing Games (MMORPGs) in many different forms, such as mob drops random dungeon drops. Variable ratio reward schedules are also commonly seen in mobile games, in an attempt increase players’ play time per session. Player reaction to this reward schedule may vary depending on how it is implemented. If a player were to receive the reward as a bonus on top of the core gameplay, instead of the reward being required for continued gameplay, the player is more likely react positively towards the game. Variable ratios are almost always identifiable when the term “chance” is involved. (Examples: Critical chance and drop chance)
Fixed interval reward schedules weaker in habituation reinforcement, but provide the developer a more predictable pattern in player behaviour. This, in turn, allows for easier game design when certain elements of a game’s mechanics need to be finely controlled. It is usually seen in the form of player logins and players leveling their character up. Players perceive fixed interval scheduling as opportunities for playing the game in the most efficient manner possible. For example, in an MMORPG the player may get additional experience points rewarded for playing the game every evening. During those hours, the player will feel compelled to play the game to maximise their efficiency in the game.
Variable Interval reward schedules are actually very rarely seen on their own in games, because player reactions towards the schedule may range from zero effect on player behaviour to discouraging the player from completing the action again, or even may even confuse the player. For example, a player may be rewarded for logging into a game after a random amount of time. The player cannot guarantee that there is a reward for completing the action unless a long time has passed and therefore they discouraged from continuing to perform the action frequently. However, this reward schedule is more often seen when layering it with another reward schedule.
Layering Reward Schedules
Reward schedules can be layered in combination with each other to achieve varying effects. The same layering techniques may not always result in the same player behaviour, as it depends on the action in which that player is rewarded for in a case-by-case scenario. A very good example of this is in the game, Warframe. In Warframe, players are rewarded for logging into the game each day (fixed interval), but the reward can vary from minor to larger rewards (variable ratio). In this case, the reward schedule is a fixed interval with a variable ratio reward schedule layered on top. It is especially important to test player reactions to layered reward schedules to judge player reactions as they may result in the opposite of the desired action. In the end, it requires player testing, but if done right, it can be a huge asset for player retention.