Dynamic Difficulty Adjustment, Is It Worth Using?
The paper “AI for Dynamic Difficulty Adjustment in Games” by Hunicke and Chapman states that “Video Games are boring when they are too easy and frustrating when they are too hard.” and that, through the use of dynamic difficulty adjustment (DDA), a game can be tailored to fit the experience and capabilities of each player as they progress through the game. This method of balance not only allows players of any experience-level to better enjoy the game, but it also enhances re-playability.
Players of all experience-levels, ranging from those who have never played a game before to professional eSports competitors, are all unique. Each player has their own play-style and knowledge which plays a role in dictating how well they perform in any given game. Many game designers take this into account through the use of various pre-set difficulty levels such as easy, medium, and hard when designing their game. These difficulty levels can affect elements such as the frequency of health/ammo drops and enemy strength. Though pre-set difficulty levels are a tried and true method of catering to a wide variety of players, they are not the best possible solution in every case. For example, imagine a procedurally generated endless-runner game similar to Temple Run where the player must navigate a unique level comprised of various obstacles and maze-like paths to reach some goal. In this example, it may make sense to allow the player to choose from easy, medium, or hard levels and to create a unique generation algorithm, or customization of a single algorithm, for each option, but these three presets can also be augmented or replaced by a dynamic difficulty adjustment (DDA) algorithm. Instead of allowing the player to choose which difficulty they would rather play on, the game can begin with an untrained DDA algorithm that slowly tests the player’s response times, success rates on overcoming each obstacle, reaching specific milestones or goals, and various other metrics. As the DDA algorithm is trained on the player’s specific metrics, it will automatically make adjustments to the spawn rates of certain obstacles, enemies, level size, required response/reaction times, and other variables of the procedural generation algorithm. Adjustments to the procedural algorithm will then cause the game to increase or lessen in difficulty as the player’s experience-level increases, decreases, or possibly when the player begins to fail too often. With a well written DDA algorithm, the game will keep the player in a constant flow state where “Challenge and pacing must ramp to match skill, in order to support continued engagement.” (Hunicke & Chapman)
Re-playability is often a forethought in game design and there are many techniques, which involve some form of procedural or randomized elements, that can be utilized and combined to create an enjoyable and uniquely re-playable experience. The previously described Temple Run-eqsue game is one example where a procedural technique or techniques, in this case procedural level generation, can be used to to give the player a unique experience on every re-play. Although procedural generation is a large topic and there are countless ways to implement such techniques, it is useful to take into consideration the benefit of a DDA algorithm used in-conjunction with procedural techniques. As previously stated, adjustments to the parameters of a procedural level generation algorithm, such as the spawn rates of certain obstacles, enemies, and level size, can be performed by a DDA algorithm to affect the difficulty of each level as the player is playing through it either in real-time or between levels. Through use of these adjustments, the DDA algorithm is effectively ensuring that each re-play of the game is not only unique, as guaranteed by the procedural algorithm, but that each re-play is both a challenge to the player to increase his or her skills and to provide an enjoyable experience that is neither frustrating or dull. As Missura et. al. have stated “The perceived difficulty of the game also contributes to the time that any given player spends playing it. Games that are too easy or too difficult become boring or frustrating fast.”
In their paper, Hunicke and Chapman are primarily working within the area of game balancing and how it can be done through the use of an automated system to cater specifically to each unique player. Traditional game balancing, as can be used with pre-set difficulty levels, is where “Game developers iteratively refine these systems based on play testing feedback – tweaking behaviors and settings until the game is balanced.” (Hunicke & Chapman). As many game developers and, more specifically, programmers may learn at one point or another, deciding the actual values to be used in a game based off of game design documentation is difficult. Terms such as “High Damage”, “Very Fast Attack”, and “Slow Movement” are vague and mean nothing until a “Normal” set of values is decided upon. Without expressed integer or decimal values, the programmer is incapable of creating a proper balance between, for example, enemy health and player attack damage. In a situation such as this, the values inserted into the game may simply be an educated guess as to what could work. By implementing some form of DDA algorithm, both the design team and the programmer can exchange the stress, work, and costs associated with iterative game balancing for the stress, work, and costs associated with developing a working DDA algorithm. An exchange such as this must be carefully analyzed as the work and costs associated with DDA development may outweigh those of traditional balancing. Games such as Bejeweled, Solitaire, and Chess may not benefit much from a DDA algorithm due to their simple and deterministic nature, but Counter Strike: Global Offensive, Torchlight II, and Diablo 3 may be able to offer a more challenging, varied, and fresh replay experience if a DDA algorithm is utilized.
In conclusion, a game can be tailored to fit the experience and capabilities of each player as they progress through the game by use of a dynamic difficulty adjustment (DDA) algorithm. Players of all experience levels can benefit from uniquely adjusted game play as the adjustments will ensure that players remain in a constant flow state which will increase both player enjoyment and therefore player retention. Though traditional iterative balancing is a tried and true method, it is not applicable to every game. DDA adjustment algorithms are a useful tool a game such as Counter Strike: Global Offensive, Torchlight II, and Diablo 3 where the player’s skill, equipment, and other factors can cause the challenge of the game to greatly lessen over time. A DDA algorithm, if properly utilized, is a powerful tool which is potentially able to save hundreds of man-hours of iterative game balancing.