D&D 3E/3.5 Confused about Level Adjustment in MM3.5

[jgbrowning]

According to MM3.5 page 7 and SRD

Level Adjustment
This line is included in the entries of creatures suitable for use as player characters or as cohorts (usually creatures with Intelligence scores of at least 3 and possessing opposable thumbs). Add this number to the creature's total Hit Dice, including class levels, to get the creature's effective character level (ECL). A character's ECL affects the experience the character earns, the amount of experience the character must have before gaining a new level, and the character's starting equipment.

How is this number determined? What is the relationship between CR and ECL?

Any advice is appreciated,

joe b.

 

[kreynolds]

How is this number determined?

Based upon the strengths and weaknesses of the creature. See Savage Species. It covers (more or less) how to determine the LA of a creature.

What is the relationship between CR and ECL?

See the latest Sage Advice (Dragon 311), or see Savage Species. Basically, ECL measures a character's power, while CR measures a monster's power.

 

[Henrix]

LA is determined by judging how powerful the creature would be as a PC. It bears no direct relation to CR, although they are related.

Mainly there's things that would add little to a creature's CR but that would add to a PC's power, like an ability to read minds, or cast Augery at will.

I don't think I have ever seen anything on how to estimate LA (or ECL), and it is mostly a matter for careful consideration and playtesting.
It is, however, better to be overly careful and overestimate LA, rather than giving a creature a LA lower than it ough to have. The other players will feel less short-changed that way.