Basic Introduction to Game Design

Chance and Skill in Game Design

Welcome to the fifth week of class in the course: Basic Introduction to Game Design. Make sure to read the syl­labus and course infor­ma­tion before you con­tin­ue. Today, we are going to dis­cuss chance and skill in game design. This text fol­lows close­ly from our text­book (Challenges for Game Designers, Chapter 5 and 8). I also take inspi­ra­tion from Schell’s The Art of Game Design (Chapter 10, pp.150–170) and Adams’s and Rollings’s Fundamentals of Game Design (Chapter 11). However, this is the part when I break free.

Games, which fea­ture mean­ing­ful deci­sions, do not always have to require or evoke skills from a play­er. Some games oper­ate entire­ly by chance. Games that rely more heav­i­ly on chance than on skill are often found in the con­text of children’s games or gam­bling. Why does this dif­fer­ence mat­ter? The play­er is going to play, play, play, play, play — are they not? Do not shake off the notion of chance too swift­ly. Games of chance can be very engag­ing, because they can allow play­ers of dif­fer­ent skill sets to engage in a bal­anced com­pe­ti­tion. Games are for every­one; for peo­ple, who are used to rolling the dice and peo­ple, who like to feel the fear in their enemy’s eyes. Some peo­ple even think it is fun to lose and to pre­tend. However, games of luck in par­tic­u­lar seem to fea­ture more attain­able goals and are winnable by more peo­ple.

On the oth­er hand, games like Tic-Tac-Toe are entire­ly skill-based and can be mas­tered, once a play­er fig­ures out a dom­i­nant strat­e­gy. See this exam­ple lec­ture for form­ing a Tic-Tac-Toe strat­e­gy via rea­son­ing:


It might seem crazy what I am about to say, but there are sev­er­al rea­sons for games to use chance as a game mechan­ic:

  • The  game design­er wants to pre­vent or delay the play­er from solv­ing the game.
  • The game design­er wants the game­play to be bal­anced and com­pet­i­tive for all dif­fer­ent kinds of play­ers.
  • Chance can increase the vari­ety of ele­ments in your game sys­tem.
  • Chance can help you cre­ate dra­mat­ic moments in your game.
  • Chance can enhance the deci­sion-mak­ing in your game.

On Game Balance

Adams and Rollings describe a bal­anced game as “fair to the play­er or play­ers, [...] nei­ther too easy nor too hard, and makes the skill of the play­er the most impor­tant fac­tor in deter­min­ing his suc­cess.” A game that is con­sid­ered well-bal­anced, there­fore, has the fol­low­ing char­ac­ter­is­tics:

  • The game pro­vides mean­ing­ful choic­es. Several strate­gies can allow the play­er to win. There is no dom­i­nant win­ning strat­e­gy in the game.
  • Chance does not play a role so great that play­er skill is irrel­e­vant. A play­er with more skill should be more suc­cess­ful than a poor play­er.
  • The game’s lev­el of dif­fi­cul­ty should be con­sis­tent. The play­ers per­ceive the chal­lenges in the game as not abrupt and with­in a rea­son­able range of their abil­i­ties.

In Player-vs-play­er games, the fol­low­ing char­ac­ter­is­tics also apply:

  • The play­ers per­ceive the game as fair.
  • Any play­er, who falls behind ear­ly in the game, gets some oppor­tu­ni­ty to catch up before the end of the game.
  • The game sel­dom or nev­er results in a stale­mate if the play­ers are of unequal abil­i­ty.

 Playtesting for luck and skill balance

When bal­anc­ing games, an impor­tant fac­tor to con­sid­er is the bal­ance of skill and luck ele­ments in the games. Some of the fol­low­ing are signs indi­cat­ing that your skill/luck bal­ance might be off:

  • Your play­ers are bored. This is gen­er­al­ly a sign of miss­ing inter­est­ing deci­sions in the game and too many luck ele­ments.
  • Your play­ers are only bored when it is not their turn. Your game is like­ly lack­ing some strate­gic ele­ments as none of the things play­ers do dur­ing their turn seem to affect oth­er play­ers’ turns.
  • Your play­ers do not become engaged in the game and are con­fused about what to do. This could be a sign of too many deci­sions or too much infor­ma­tion to process for play­ers.
  • One of your play­ers beats all the oth­er play­ers by a wide mar­gin. This could be an indi­ca­tor that your game is heav­i­ly skill-based and one play­er has mas­tered this skill. To keep a game bal­anced for play­ers with dif­fer­ent skill lev­els, it is impor­tant to add some ele­ments of luck to it.

Generally, adding “luck” to a game comes down to adding ele­ments of ran­dom­ness. In board games, this is often done through dice rolls or shuf­fling cards. If you find that you are using too many of these ran­dom ele­ments, you can replace them by using dis­tinct auto­mat­ed advances (e.g., mov­ing a play­er token a dis­tinct num­ber of spaces dur­ing a turn) or by adding a play­er deci­sion instead of the ran­dom ele­ment (e.g., play­ers can choose from a giv­en range of move­ment options). Player deci­sions are not just com­plex think­ing deci­sions at all times, but can also be split-sec­ond dex­ter­i­ty-based deci­sions (twitch skills like hit­ting notes in Guitar Hero).

Our text­book (Challenges for Game Designers) dis­tin­guish­es between three types of luck/skill games:

  1. Games of chance. This can be either children’s games or gam­bling games. These games can often be enhanced by adding twitch and strate­gic ele­ments to them. Often just the illu­sion of skill in those games is enough to make them more inter­est­ing.
  2. Games of twitch skill. These are games that are focused on a chal­lenge of dex­ter­i­ty. These games tend not to work too well with chance ele­ments, but adding sim­ple tac­ti­cal options is quite com­mon. Anything that keeps the flow of the game is a pos­si­ble addi­tion.
  3. Games of strate­gic skill. These games can feel tense and slow, because they involve a lot of think­ing. Adding twitch ele­ments can be a wel­come inter­rup­tion of these long strate­gic ses­sions. Many long-wind­ed RPGs fea­ture lit­tle twitch mini games (such as lock­pick­ing in Skyrim) to inter­rupt some of the longer stretch­es.

Types of Skills

Jesse Schell dis­tin­guish­es between three main cat­e­gories of skill in his Art of Game Design book. Keep in mind that many games require a blend of dif­fer­ent skills, but these cat­e­gories pro­vide a start­ing point:

  1. Physical skills: Skills like dex­ter­i­ty, coör­di­na­tion, strength, and phys­i­cal endurance. These types of skills are most com­mon­ly found in sports games. However, some might argue that the cor­rect key­press and con­troller sequences found in some esports would also fall into this cat­e­go­ry.
  2. Mental skills: Skills like obser­va­tion, mem­o­ry, and puz­zle solv­ing. Often these relate to mak­ing inter­est­ing deci­sions in a game, as most inter­est­ing deci­sions are also tac­ti­cal deci­sions.
  3. Social skills: Skills like read­ing an oppo­nent, trick­ing an oppo­nent, and coör­di­nat­ing with team­mates. These relate to a player’s abil­i­ty to make friends and influ­ence peo­ple in a game. They are often tied to a player’s com­mu­ni­ca­tion skills. This is also com­mon­ly seen in team-based sports.

Schell also dis­tin­guish­es between real skill, which means your actu­al skill as a human per­son in con­trol­ling the game in a cer­tain way, and vir­tu­al skill, which relates to your in-game character’s skill at doing some­thing. Real skills only improve when you work on them, while vir­tu­al skills can improve even when your real skill does not improve. In gen­er­al, Schell sug­gests mak­ing a list of all skills in your game as an exer­cise to break down your game into skill com­po­nents.  Finding out what skills you require from your play­ers will make you a bet­ter design­er.


Chance can make games more fun, because it adds ele­ments of uncer­tain­ty to it. Uncertainty equal sur­pris­es for play­ers and humans do enjoy sur­pris­es. Chance is also relat­ed direct­ly to prob­a­bil­i­ty in games, and Schell lists ten rules of prob­a­bil­i­ty with which game design­ers should be famil­iar:

  1. Fractions are dec­i­mals are per­cents. Fractions, dec­i­mals, and per­cents essen­tial­ly all work the same way and are essen­tial­ly the same thing: 1/2 = 0.5 = 50%. As humans, we like to express prob­a­bil­i­ties in per­cent­ages.
  2. Zero to one — and that’s it. This con­cerns, of course, prob­a­bil­i­ties, which all hap­pen in the space between 0 and 1 (i.e., 100%). Chances like -10% or 110% do not exist when we speak about prob­a­bil­i­ties in games. If you are try­ing to cal­cu­late the prob­a­bil­i­ties of your dice rolls and they come up high­er than 100, you know that you will need to run your cal­cu­la­tion again.
  3. Looked for” divid­ed by “pos­si­ble out­comes” equals prob­a­bil­i­ty. Probability real­ly means you take the num­ber of times the out­come that you are look­ing for can (or has) come up and divide this by the num­ber of pos­si­ble out­comes (in the case that all out­comes are sim­i­lar­ly like­ly) .
  4. Enumerate. Let’s say that you are try­ing to find the out­comes that you are look­ing for and it is not as straight­for­ward as the num­bers on a D6; a good way of get­ting to your answer is just to list all the pos­si­ble out­comes in your sce­nario. This helps you see pat­terns and com­bi­na­tions.
  5. In cer­tain cas­es, OR means ADD. When try­ing to deter­mine the chances of x or y hap­pen­ing (like draw­ing cer­tain cards from a deck) and these events are mutu­al­ly exclu­sive, you can add the prob­a­bil­i­ties to get the over­all prob­a­bil­i­ty of an OR event.
  6. In cer­tain cas­es, AND means MULTIPLY. When we are look­ing for the prob­a­bil­i­ty of two things hap­pen­ing simul­ta­ne­ous­ly, we can mul­ti­ply their prob­a­bil­i­ties. This only works if the two events are NOT mutu­al­ly exclu­sive.
  7. One minus “does” equals “doesn’t.” This quite log­i­cal as 1 rep­re­sents a 100% chance of some­thing hap­pen­ing. So, when­ev­er you have cal­cu­lat­ed the prob­a­bil­i­ty of some­thing occur­ring, you can sub­tract this num­ber from 1 to find the prob­a­bil­i­ty of the oppo­site event occur­ring.
  8. The sum of mul­ti­ple lin­ear ran­dom selec­tions is NOT a lin­ear ran­dom selec­tion. By lin­ear ran­dom selec­tion, we are refer­ring to a ran­dom event where all the out­comes have an equal chance of occur­ring. A die roll is a great exam­ple of this. Adding mul­ti­ple die rolls does not mean that the pos­si­ble out­comes have an equal chance of occur­ring. Rolling a die twice means that you have a high­er chance of a sev­en occur­ring. The pos­si­ble out­comes of this sce­nario fol­low a prob­a­bil­i­ty dis­tri­b­u­tion curve (a nor­mal dis­tri­b­u­tion in this case), where the num­bers in the mid­dle (6,7,8) have a high­er like­li­hood of com­ing up.
  9. Roll the die. Schell dis­tin­guish­es between the­o­ret­i­cal prob­a­bil­i­ty and prac­ti­cal prob­a­bil­i­ty. Theoretical prob­a­bil­i­ty is what we have talked about so far. It is what is like­ly to hap­pen in a gen­er­al case. However, prac­ti­cal prob­a­bil­i­ty accounts for what has already hap­pened. For this you would just roll a die over and over and record the num­ber that you are get­ting and cal­cu­late your prob­a­bil­i­ty based on this. Ideally, this prob­a­bil­i­ty should approach the the­o­ret­i­cal prob­a­bil­i­ty with a repeat­ed num­ber of tri­als. This is also known as the Monte Carlo method.
  10. Geeks love show­ing off (Gombauld’s law). Schell basi­cal­ly rec­om­mends to find a math wiz friend, when­ev­er you are fac­ing a prob­a­bil­i­ty prob­lem that you can­not solve on your own. This can also include post­ing math and prob­a­bil­i­ty relat­ed ques­tions to mail­ing lists.

Some impor­tant things to remem­ber about chance are (from Adams and Rollings):

  • Use chance spar­ing­ly.
  • Use chance in fre­quent chal­lenges with small risks and rewards.
  • Allow the play­er to choose actions to use the odds to their advan­tage.
  • Allow the play­er to decide how much to risk.

Further Reading

Am I miss­ing some­thing? Write a com­ment to this post at the very bot­tom of the page.

  1. Making Sense of Complexity. Brice Fernandes (2014). Gamasutra.
  2. Design in Detail: Changing the Time Between Shots for the Sniper Rifle from 0.5 to 0.7 Seconds for Halo 3. Jaime Griesemer (2010). GDC Vault Video.
  3. On Difficulty Levels. Ben “Yahtzee” Croshaw (2010). Extra Punctuation.
  4. Playing Fair: A Look at Competition in Gaming. Mark Newheiser (2009).
  5. An atom­ic the­o­ry of fun game design. Raph Koster (2012). See also: Grammar of game­play.
  6. The Mathematical Structure of Possibility. Mark Neyer (2014).

Further Viewing


2 thoughts on “Chance and Skill in Game Design

  1. Pingback: Animal Crossing – Create. build. game.

  2. Pingback: Create. build. game.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.