Quote Originally Posted by Niwashi View Post
If everyone in the group is there through Roulette, then a dungeon will be selected randomly, but it will be random from the set that everyone in the group has unlocked. Any group with at least one low-level character will of course have to get a low-level dungeon, even if the other 3 members are level 50. Add that chance to the fact that even when all members are high level, those same low-level dungeons are included in the random possibilities, and you end up with a higher "random" chance of getting low level dungeons than higher level ones, just because more characters will have access to the low-level ones.
It's random but chances get skewed based on how many people are in each dungeon. If your entire party is queued for roulette you will be more likely to enter dungeons that currently have less people running them in order to spread out the players and ease server stress.