Player profiling for balancing level content and gameplay

Play Personas are used for designing gameplay experiences that cover a broad range of potential players and behaviors, even before prototyping.

The "personas" combine psychological profiling of possible player types in relation to the activities or interactions in the game.

The profiling uses Mayers-Brigs personality tests and can be done either with actual testers during closed alpha, or with focus groups from the target audience before production has even begun.

To establish the player types the development team must have settled down on the core mechanics of the game.  These are then listed and grouped into "activity groups" - exploration, combat, roleplay, socializing, etc.

The possible combinations of these activities form the potential 
player types which are profiled. Afterwards a Mayers-Briggs test is filled for each type to identify what profile they possess. 

The resulting personas are then expanded by exploring the specific preferences and affinities towards things such as colors, shapes or psycho-acoustic predispositions, attention retention, gameplay behavior and others.

The above findings can be directly applied to balance and "player proof" the gameplay posibilities of an area , balance a particular mechanic or ensure the appeal of a certain environment to a wide variety of players.
The Personas can then be combined with other player-centric design techniques like "A-B testing" or "7 Sins design" to ensure a strong engagment loop for as many players as possile.
 

References

Canossa,A. [2009] "Play-Persona: Modeling Player Behaviour in Computer Games"  DDS

Drachen,A. and Canossa,A.[2009] "Patterns of Play: Play-Personas in User-Centred Game Development "  in "Proceedings of DiGRA 2009"