Wednesday, May 15, 2013

Advancement, Progression and Pacing (Part IV)

In Part I of this article, game designer and educator Ian Schreiber explains the reasoning behind using advancement, progression and pacing in games. In Part II, he discusses challenge levels in PvE.  In Part III, he explains how to handle the reward schedule in PvE.  Next, he tackles challenge levels in PvP.

Challenge Levels in PvP 

 If PvE games are all about progression and rewards, PvP games are about gains and losses relative to your opponents. Either directly or indirectly, the goal is to gain enough power to win the game, and there is some kind of tug-of-war between the players as each is trying to get there first. I’ll remind you that when I’m saying “power” in the context of progression, I’m talking about the sum of all aspects of the player’s position in the game, so this includes having more pieces and cards put into play, more resources, better board position, taking more turns or actions, or really anything that affects the player’s standing (other than the player’s skill level at playing the game). The victory condition for the game is sometimes to reach a certain level of power directly; sometimes it is indirect, where the actual condition is something abstract like Victory Points, and it is the player’s power in the game that merely enables them to score those Victory Points. And in some cases the players don’t gain power, they lose power, and the object of the game is to get the opponent(s) to run out first. In any case, gaining power relative to your opponents is usually an important player goal.

Tracking player power as the game progresses (that is, seeing how power changes over time in a real-time game, or how it changes each turn in a turn-based game) can follow a lot of different patterns in PvP games. In PvE you almost always see an increase in absolute player power level over time (even if their power level relative to the challenges around them may increase or decrease, depending on the game). In PvP, there are more options to play with, since everything is relative to the opponents and not compared with some absolute “You must be THIS GOOD to win the game” yardstick.

Positive-sum, negative-sum, and zero-sum games

Here is an important distinction in power-based progression that we borrow from the field of Game Theory: whether the game is zero-sum, positive-sum, or negative-sum. If you haven’t heard these terms before:
  • Positive-sum means that the overall power in the game increases over time. Settlers of Catan is an example of a positive-sum game: With each roll of the dice, resources are generated for the players, and all players can gain power simultaneously without any of their opponents losing power. Monopoly is another example of a positive-sum game, because on average every trip around the board will give the player $200 (and that money comes from the bank, not from other players). While there are a few spaces that remove wealth from the game and are therefore negative-sum (Income Tax, Luxury Tax, a few of the Chance and Community Chest cards, unmortgaging properties, and sometimes Jail), on average these losses add up to less than $200, so on average more wealth is created than removed over time. Some players use house rules that give jackpots on Free Parking or landing exactly on Go, which make the game even more positive-sum. While you can lose lots of money to other players by landing on their properties, that activity itself is zero-sum (one player is losing money, another player is gaining the exact same amount). This helps explain why Monopoly feels to most people like it takes forever: it’s a positive-sum game so the average wealth of players is increasing over time, but the object of the game is to bankrupt your opponents which can only be done through zero-sum methods. And the house rules most people play with just increase the positive-sum nature of the game, making the problem worse!
  • Zero-sum means that the sum of all power in the game is a constant, and can neither be created nor destroyed by players. In other words, the only way for me to gain power is to take it from another player, and I gain exactly as much as they lose. Poker is an example of a zero-sum game, because the only way to win money is to take it from other players, and you win exactly as much as the total that everyone else loses. (If you play in a casino or online where the House takes a percentage of each pot, it actually becomes a negative-sum game for the players.)
  • Negative-sum means that over time, players actually lose more power than they gain; player actions remove power from the game without replacing it. Chess is a good example of a negative-sum game; generally over time, your force is getting smaller. Capturing your opponent’s pieces does not give those pieces to you, it removes them from the board. Chess has no zero-sum elements, where capturing an enemy piece gives that piece to you (although the related game Shogi does work this way, and has extremely different play dynamics as a result). Chess does have one positive-sum element, pawn promotion, but that generally happens rarely and only in the end game, and serves the important purpose of adding a positive feedback loop to bring the game to a close.
An interesting property here is that changes in player power, whether zero-sum, positive-sum, or negative-sum, are the primary rewards in a PvP game. The player feels rewarded because they have gained power relative to their opponents, so they feel like they have a better chance of winning after making a particularly good move.

Positive and negative feedback loops

Another thing I should mention here is how positive and negative feedback loops fit in with this, because you can have either kind of feedback loop with a zero-sum, positive-sum or negative-sum game, but they work differently. In case you’re not familiar with these terms, “positive feedback loop” means that receiving a power reward makes it more likely that you’ll receive more, in other words it rewards you for doing well and punishes you for doing poorly; “negative feedback loop” is the opposite, where receiving a power reward makes it less likely you’ll receive more, so it punishes you for doing well and rewards you for doing poorly.

One interesting property of feedback loops is how they affect the player’s power curve. With negative feedback, the power curve of one player usually depends on their opponent’s power: they will increase more when behind, and decrease more when ahead, so a single player’s power curve can look very different depending on how they’re doing relative to their opponents, and this will look different from game to game.

With positive feedback, you tend to have a curve that gets more sharply increasing or decreasing over time, with larger swings in the endgame; unlike negative feedback, a positive feedback curve doesn’t always take the opponent’s standings into account… it can just reward a player’s absolute power.
Now, these aren’t hard-and-fast rules… a negative feedback loop can be absolute, which basically forces everyone to slow down around the time they reach the end game; and a positive feedback loop can be relative, where you gain power when you’re in the lead. However, if we understand the game design purpose that is served by feedback loops, we’ll see why positive feedback is usually independent of the opponents, while negative feedback is usually dependent.

The purpose of feedback loops in game design

The primary purpose of positive feedback is to get the game to end quickly. Once a winner has been decided and a player is too far ahead, you don’t want to drag it out because that wastes everyone’s time. Because of this, you want all players on an accelerating curve in the end game. It doesn’t really matter who is ahead; the purpose is to get the game to end, and as long as everyone gets more power, it will end faster.

By contrast, the primary purpose of negative feedback is to let players who are behind catch up, so that no one ever feels like they are in a position where they can’t possibly win. If everyone is slowed down in exactly the same fashion in the endgame, that doesn’t fulfill this purpose; someone who was behind at the beginning can still be behind at the end, and even though the gap appears to close, they are slowed down as much as anyone else. In order to truly allow those who are behind to catch up, the game has to be able to tell the difference between someone who is behind and someone who is ahead.

[This article was adapted from Ian Schreiber's course, Game Balance Concepts.]

Ian Schreiber has been in the game industry since the year 2000, first as a programmer and then as a game designer. Also an educator since 2006, Ian has taught game design and development courses at a variety of schools, and on his own without a school. He has co-authored two books, Challenges for Game Designers and Breaking Into the Game Industry.  


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