Designing Strategy: Hidden Information

by Shannon Appelcline

March 20, 2003 – It's been three weeks, but having finished talking about publication and its relation to our new Associate Games program, I'm ready to jump right back into strategy games. This week I want to cover a topic that I hadn't originally planned for: information. Its absence was called to my attention over on RPGnet back when I was talking about components.

Thus far I've presented games pretty simply, imagining that everyone sees the same pieces sitting on the same game board. But, that's not always the case. Generally, I think of using hidden information as a somewhat uncommon technique in the main vein of (non-card) tabletop strategy games, but it's interesting to note that many of the most popular strategic games out there depend upon hidden information of some type. Just about every traditional card game does; Go Fish makes the secrecy part of the game play, Poker partially obscures information to create more interesting betting dynamics, and Bridge hides cards but forces players to bid which causes partial revelation. Popular board games which depend upon hidden information include Battleship, Clue(do), Concentration, Mastermind, and Stratego.

The basic technique of hidden information is simply to hide some aspect of the game from some of the players. However, as with everything in strategic game design, there are many possibilities.

Why?

The first question is clearly: why would you hide information?

In my opinion, doing so creates a whole new level of interaction in your game. You have the textual level of play, where players are interacting with each other and with the game system based on what they see. But you also have a subtextual level of play where you're trying to figure out what information other players might know based on their cues — and what information might be hidden by the game system based on your own statistical analysis.

I think Poker in two of its variants provides the best example of why hidden information is cool.

First, consider 5-card draw. You draw some cards which no one else sees, then you bet, then you draw some more cards that no one else sees, then you bet, then everyone reveals cards and someone wins. You have your textual level of play where you're trying to figure out how to better your hand, but there's almost no subtext — no real strategizing on what other players might have, because their bets have almost no meaning without context. Frankly, I consider 5-card draw a random and boring game.

Then, consider 7-card stud. You get two cards down, then four cards up, then one more down, and betting occurs throughout. There's the textual level of play, where you decide whether to stay in or not, based on what cards you have, and what your probabilities are of improving that hand based on the number of cards left and what everyone else is showing. But now there's a strong subtextual level where you consider what each player is showing and how they're betting and what it says about what they may or may not have.

There's a whole language of subtext in Poker, from "tells", where a player might accidently give away his hidden information through a habit, to the well-known idea of a "bluff".

Falling back on some of my earlier language for strategic games, I'd say that hidden information allows you to notably increase the complexity of a game, by giving players many more options to consider, but does it in a way that's invisible to the casual player, thus offering the best of both worlds: playability and strategy.

Who?

The next question is: who gets to hold onto hidden information?

Most commonly, individual players get to hold onto hidden information, without it being seen by anyone else. Any card game provides a good example here, with each player only seeing his own hidden cards.

Sometimes, however, the game system itself holds on to the information, until it's revealed either to individual players or to everyone. Concentration and Clue(do) both involve the game system hiding away information from players.

Another variant might allow a set of players to know a specific piece of information, but not all of the players, as a whole. Theoretically, any game which allows players to show each other their hidden information would fall into this category, but generally it's less common that the other two methods.

All of these questions of who are also closely related to the next query...

What?

... which is: what pieces are hidden?

Really, any of the standard components that I laid out in Trials, Triumphs & Trivialities #102, Designing Strategy: The Components can be hidden. This includes: tokens, markers, or the environment. However, there are a number of fairly standard ways to hide component information, which I've outlined below:

Hidden Arbitrary Tokens: Because they don't tend to be associated with any environment, it's the easiest to hide arbitrary tokens (which is to say cards). Almost every card game hides a set of cards in the player's hand: Bridge, Euchre, Hearts, Poker, Rummy, etc., etc. Most traditional board games which involve cards also hide those cards' value. For example you can accumulate development cards in The Settlers of Catan but other players don't know their value until you play them. Tigris & Euphrates is another example of a game which hides the value of arbitrary tokens, though in this case they're tiles rather than cards.

Other Hidden Tokens: The hiding of other types of tokens is less common in traditional tabletop games because they tend to be associated with the environment, and it's hard for players to each have their own view of the environment, as I'll discuss further in the how section, below. Battleship is an example of a game where each player can only see his set of tokens, and it's pretty rare.

Hidden Token Values: Slightly more common is hiding the value of a token, but not the token itself. This lets you have a common environment that everyone can see without the risk of giving away information. Stratego shows this type of hidden information, in a rather cleverly crafted method. Many war games also hide token value.

Hidden Victory Markers: Just as with arbitrary tokens, it's pretty easy to hide markers because they're usually not associated with the environment and thus don't cause perception problems. Many games hide some or all victory markers, partially as a method of reducing some of the end game problems that I mentioned in my last column on strategy. Tigris & Euphrates has you place your victory markers behind a screen as you gain them. The Settlers of Catan lets you accumulate some victory points in development cards, which are hidden; thus, while other players might be able to see 80-90% of your VPs, they can never measure them exactly.

Other Hidden Markers: Any other type of marker can be hidden as well. Most games don't let you count other players' money (a trade marker), for example. You could likewise easily hide power markers until they were used... or just about any thing else which isn't on the board itself.

Hidden Environment: Less common than some of the above is hiding parts of the actual game environment. Typically this is done in randomized environments which are revealed during game play. I'd classify an evolutionary environment as likewise hidden, even though it technically doesn't exist before it's displayed. However, whether a map segment is placed on your tabletop and upside down, or whether you actually randomize it during gameplay, it's unknown until someone takes whatever action is necessary to bring it into existence.

Hidden Gameplay Information: Finally, you have games where the hiding of information and its eventual revelation is the whole point of the game. For example in Clue(do) there's a hidden murderer, murder weapon, and murder location; the whole game is about revealing that information. In Concentration you're trying to remember hidden information in order to win the game. In Mastermind you're following certain rules in order to figure out what pegs have been played (In many ways, this isn't too different from the gameplay of Battleship, showing that all of these classifications are ultimately arbitrary.)

How?

So: how do you actually include this hidden information in your game? Traditional tabletop games have tended to use the following methods:

Two-Sided Token: Perhaps the most common way to hide information. This tends to work great if you're just hiding the values of things, and not their actual existence. Thus you tend to be able to use this technique to hide environment, to hide token values, and to hide the values of markers of all types.

War games tend to include cardboard chits which sometimes have two sides: a side without values, which says there's an army here, and a side with values, which says what that army does. Stratego uses the same strategy except rather than putting the information face-down it points the value information toward the controlling player. Clearly this method breaks down when you have more than two players, and thus the producers have been forced to adopt a more complicated tower-design for the newer four-player version of the game.

In games with hidden environment you tend to have face-down tiles or hexes which are flipped face up when revealed.

Most card games fall into this category too, because there's a non-descript back and a front with actual information.

Hidden Details Listing: In this scenario you have a token labeled, e.g., "X1" on the board, and then a sheet of paper that you can only see which lists exactly what "X1" does and means; overall, this is very similar to the two-sided technique, has the benefit of your not having to reveal which tokens you're interested in by flipping them over, but has the deficit of being a little less clean and feeling a little bit less like a cohesive unit.

Information Screen: A somewhat less common technique. In this case you have some physical barrier which blocks what other people can see. Tigris & Euphrates uses a screen to hide your victory points and your current tiles while Fist of Dragonstones uses a screen to hide which coins you still have available for auction. The old Avalon Hill Dune game used screens to hide all sorts of semi-secret tokens and markers which weren't on the board.

I suppose you could say that Clue(do) does the same thing. In this case there's an envelope which contains information that none of the players get to see... until the very end.

Multiple Boards: In this scenario each players gets to see a unique board showing only what he knows. This is ultimately impractical in most games because, first of all, you need to have either N boards, 1 for each of N players, or even worse N^2 boards, 1 for each set of two players. Secondly, you usually need to have an arbitrator to help keep all the information straight. Battleship is a rare game which manages these challenges by only allowing two players and by using the gameplay to reveal information. Online games tend to be better at this sort of thing, as I'll discuss more in a bit.

When?

Ultimately the two cores of hidden information are the question I've already answered, on what you hide, and the question of when you reveal that hidden information.

There are three methods which I consider full revelation, because they involve actually showing information rather than just hinting at it:

At Usage: You fully reveal hidden information when you make use of that hidden information, most frequently when you play a card or place a token on the board or whatever. Concentration offers another example, where you reveal the hidden information when you claim it because you've made a match. Many games also center this usage around conflict. For example in Stratego you must fully reveal the value of a specific piece when it's attacked.

At End Game: You fully reveal hidden information when it becomes relevant because the game is ending. Clue(do) lets you reveal the details of the murder when you figure it out; Tigris & Euphrates has everyone reveal their victory markers when the game reaches its natural end.

At Forced Revelation: You fully reveal hidden information when another player makes you, usually by playing some card or using some power. For example, Titan: The Arena has a special card which forces players to reveal secret bets associated with a particular arena fighter. Clue(do) also shows this method of partial revelation, since after you suggest a murder scenario, each player shows you cards which disprove that theory.

Much more interesting is the idea of partial revelation, where you hint at information without showing it. This helps create that subtext that I've already discussed, and thus adds a new, but optional, level of complexity to your game. Ways to force partial revelation include:

Bidding: This strategy is typical used in card games, where players tend to bid how many tricks they'll be able to take with what suits trump. Bridge is the most interesting example of this, because it's allowed bidding to develop into a sort of language where partners reveal to each other what cards they have... and where opponents can try and figure out what that same linguistic discourse means.

Betting: A close cousin to bidding, where instead of bidding how much you can take with your current tokens, you're instead saying how much faith you put in those tokens through monetary bids. Poker is the obvious example of a bidding game.

Peer-to-Peer Trading: Partial revelation is forced through one-to-one exchange of desirable or undesirable cards. For example in Hearts you trade some cards at start and thus know a little bit about other players' hands — not just what they gave you, which is technically fully revelation, but more importantly what they wanted to get rid of and thus what they wanted to keep. Gang of Four shows an even more clear example. The previous loser gives the previous winner his best card, and thus you know some precise info about the rest of his hand (none of them are greater than "X" value.)

Requesting: Some games force the players to reveal themselves by giving them opportunities to request things that they want. Observant players can immediately turn this on its head, assuming that items that players are requesting reveal either strengths or weaknesses in their hidden information. Go Fish is an example of this. A more complex example is Res Publica, where each turn you try and initiate a trade, either offering specific card(s) or requesting specific card(s).

Any game which allows partial revelation can be made even more interesting if you build the ability for players to mask their hidden information — which means that they have some way to imply that the partial information revealed isn't what it seems at all. I broadly split masking into two categories:

Misleading Questions: The game offers a way for players to ask questions which reveal hidden information, and also lets players ask "silly" questions to offer wrong assumptions about the hidden information that they themselves hold. Clue(do) is the best example of this: you can ask whether a murder was done with some card that you hold, and thus imply to players that that card was a real murder detail, rather than a card held in your own hand.

Misleading Answers: When you know information is going to be revealed you can try and stage it in such a way that it doesn't give quite the right answer. For example, in Stratego you could place a couple of bombs far from your flag to mislead your opponent into defusing the wrong section of the board. In Skotos' Galactic Emperor: Hegemony players only see enemy ships when they're being attacked, not when an enemy is moving ships around his own planets; thus it's a (somewhat) common tactic to attack with enough ships to take a planet, then to move the rest in afterward.

I'd like to offer one caveat on when before I close up. A lot of hidden information games have an input/output problem. If all players get to see hidden information when a player initially hides it, you're creating a memory game instead of a strategy game (technically Concentration actually fits into this category). You're thus making the winner the person who works the hardest to remember things (or who writes copious notes), and that's usually not a desirable result.

Tigris & Euphrates displays this flaw because each player can see victory points when a player earns them and, worse, gets to see players turn in 1 point VP cubes for 5 point cubes.

This problem is annoying enough in Blackjack that dealers are forced to mix multiple decks and casinos tend to throw out card counters.

Where?

So finally we come to the question of: where can you use hidden information? Technically, any tabletop strategy game can do it, and most of the how methods that I outlined above are drawn from that medium.

However, hidden information is one of the places where web games really shine; a computer can maintain separate "boards" for every player, and a computer can also arbitrate the release of information.

Thus, if you're creating a web game, you should consider how you're going to manage hidden information to a much greater extent than you would for a tabletop game... because it's a power of the medium.

Whatever!

Before I finish up, I want to briefly revisit a couple of the examples I've been using along the way, to give a slightly more complete impression of how hidden information interacts with the various game systems that I've been discussing thus far in this series. I decided not to further exemplify games like Battleship, Clue(do), Concentration, and Mastermind, because the idea of hidden information is so central to those games that it is the game. However, games that use hidden information somewhat piecemeal can be more interesting to pull apart.

The Settlers of Catan is regularly my favorite example. See Trials, Triumphs & Trivialities #107, Anatomy of a Game: The Settlers of Catan for a complete description of it.

In Settlers you have only two bits of hidden information: resource cards (trading markers) and development cards (arbitrary tokens).

The resource cards are drawn into your hand every time the dice are rolled for production. It suffers from the classic input/output problem that I already described, but the turnover of cards is so rapid that no one really tries to memorize exactly what cards a player has. In addition, the board acts as a sort of mnemonic, because you can see which resources a player controls and thus generate a pretty good guess at what cards that player has. Together these factors allow above-board input and output of cards without creating the problems usually associated with it.

The benefit of hiding resource cards is that you never know quite what the other players are up to. If someone is trying to build a city and just needs one more ore, you're more likely to give it to him, knowing only that he wants an ore, than if you knew he would build a city immediately thereafter. It thus sort of creates a trading subgame where you can concentrate only on getting what you want without having to think about how it will affect other players' gameplay success; the result is a solid division between the different types of gameplay, thus separating the decision sets.

The development cards can be purchased from the bank. They come into your hand face down and thus are invisible to other players until they're played.

Development cards offer two real benefits in a game. Firstly, some give you the ability to undertake a surprise action (such as stealing all of a resource), thus increasing the chaotic unpredictability of the game, for which see my article on randomness. Secondly, some give you secret victory points, which helps resolve end game problems. A player is less likely to feel like he's out of the game if he can't entirely count how close someone else is.

The subtextual level of strategy that I've mentioned is actually pretty small in The Settlers of Catan. You might do some guessing at what cards a player is holding and what he's going to do, but it's minor. Instead, what the hidden information in Settlers does do is help solve some common game design problems. Decision sets are split up, chaotic unpredictability is increased, and end game boredom is reduced, all thanks to a few hidden cards.

Galactic Emperor: Hegemony, at Skotos, is a game which makes heavier use of the subtextual level of hidden information. As I've already mentioned, you get to see fleets attacking you, but not fleets moving within another player's territory.

This results in interesting "masking" strategies during play. If I attack a poorly defended world, I'm likely to attack with a small fleet to take out the defenders, then send a larger fleet in afterward, to bounce further into my enemy's space, without him knowing it's there.

Likewise, I might use threats or a singular attack to imply that my fleets are on one side of the galaxy when they're actually on another.

This all does create subtextual strategy, because I have to figure out how much subterfuge a player is using in his own fleet movements. Is he the type of player that masks? If so, does he appear to have the resources to carry out the attacks that his movements imply? Or, alternatively, if I see planets changing hands between two other players, are they really fighting, or are they just staging a fight to imply conflict?

The mind boggles...

Hegemony also uses the forced revelation method that I described earlier. You can send off spy probes to reveal ships on a particular planet, which can help imply fleet buildups. However, that becomes part of the strategy too, because these spy probes cost money that could have instead been spent on new fleet factories or technology.

Conclusion

When you're designing hidden information into a strategy game, you're biggest questions need to be what information will be hidden and when you're going to reveal it. The how will probably follow naturally (or else you'll learn that physical constraints in a tabletop game make it impossible).

And that's it for me this week. Next week I plan to offer an overview and conclusion on this series of articles. And then, in weeks to come, I'll talk a bit more about how strategic designs can relate to other mediums, such as roleplaying games and those web games which have danced in and out of this discussion.

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