Greg's Design Blog

A collection of posts by game designer Gregory Carslaw, including mirrors of all of his blogs maintained for particular projects. A complete index of posts can be found here:
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How people experience probability

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Original Post

There are certain types of mental abnormalities that cause people to leap to conclusions without sufficient information. This can lead sufferers to develop exotic beliefs based on observations that others might dismiss as coincidence, for instance "My milkman has arrived exactly an hour after Mrs. Jones dogs went for a walk two days in a row, clearly my milkman is the dog in human form.".

One way to detect this type of thinking is with a task in which participants draw marbles from a bag and must guess the nature of the bag. They know that either the bag is half and half red and green marbles where the second contains eighty percent red marbles. How many marbles a person feels the need to draw before they feel sure they know which bag they're drawing from lets you know the extent to which that person jumps to conclusions in this way. People with paranoid delusions will make their decision after just a couple of draws where a "normal" person might need half a dozen.

It is possible to work out how many draws a person should make before making their decision, at the five percent margin of error so beloved by soft scientists. On performing this calculation it becomes apparent that our conspiracy theorists are actually closer to a correct answer than everyone else. It turns out that people have a very cautious bias that, in this case, generally makes them wait too long before drawing a conclusion. This is just one of the many ways in which the normal mind is misleading. A completely healthy brain will also hallucinate on a fairly regular basis and can be trivially induced to do so.

So what does all of this have to do with game design? Well a fair bit in fact, game design is about crafting a particular experience for the player. In a two player game people experience "take another turn" differently form "make your opponent miss a turn" despite them being functionally identical. Often there are choices to be made in design that are mathematically similar but provoke different reactions from the player, when these come up knowing how the mind will misrepresent these situations can be handy.

Iowa gambling task studies challenge a participant to maximise their score by drawing cards from several decks of cards. Each card will change the participants score, either giving points or taking them away. The decks are configured differently, some decks are worse overall, some are equally good but offer their rewards in different ways. Most people will gravitate towards the "good" decks over time, but within that category prefer a certain type of reward. Specifically people tend to choose decks where they get a positive card most of the time, even if the deck is not strictly the best since the values on the positive cards in that deck are small and the values on the negative cards are high.

In terms of designing games this might suggest that players will naturally favour a strategy in which they routinely make small gains even if it is less effective than other strategies overall. I think this is partly to blame for the extent to which new players often underestimate farmers in Carcassonne. As a designer I see two ways to use this knowledge, the first is to make strategies that people instinctively choose less good than the best strategies, to create a game that rewards clear tactical thinking and has more apparent depth. The second is to create games that lead players to exclusively use competing strategies that instinctively feel good for different reasons, to try to make a game that's more rewarding to play overall.

There are a host of other ways in which the brain misrepresents probability, perhaps I'll get into them some other day. For now enjoy your games and try not to think too hard about how you can't trust anything that your brain tells you.
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