Rank

Rank is a term used to describe the difficulty of an opponent relative to The Wardens level.

Description
In Dragon Age: Origins, hostile creatures are assigned one of five ranks: critter, normal, lieutenant, boss, and elite boss. Rank determines the color of an opponent’s name - with normal creatures labeled in white text, lieutenants labeled in yellow, and bosses labeled in orange. Developers use rank to balance encounters without knowing what the level of the protagonist will be; that is to say, the level (and respective ability/skill/etc set) of enemies will be approximately equal (plus or minus) to the players, various other factors withstanding (scripted encounters, etc).

Critter
Easy creatures which are significantly less powerful than a single party member - the party must fight a large group of them for the encounter to be a significant challenge.

Lieutenant
These creatures are roughly equal to a single party member in power, and even odds will be a difficult fight.

Bosses
Bosses are designed to provide a challenge for the entire party. The difficulty of a boss may be due to unique abilities, high hit points or regeneration, traps surrounding the encounter, a particular scripting that gives them unique capabilities, or any of a number of things. Obvious examples include the High Dragon or Archdemon.

Formula
The rank formula is:

min (max_creature_type_level, min (max (party_level +/- rank_modifier, min_area_level), max_area_level)) Note that the implication here is that the relative lethality of the enemy adjusts to match the party's level, but the enemies' level is restricted from being too low or too high for the intended difficulty of the area.