3d6 is not less swingy than d20

With tabletop roleplaying game (RPG) systems, sometimes I hear a claim that bell curve dice rolls, e.g. 3d6, are “less swingy” (less variance) than a linear based dice roll such as d20 or d%.

This is, however, incorrect.

While the distribution of dice rolls are different, the distribution of outcomes – success or failure – are the same, and for equivalent circumstances have the same statistical variance / standard deviation.

Although the outcomes have equivalent distributions, the underlying type of dice system is important for analysis of modifiers and skill progression.

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