. .

I'm not too familiar with it, but there must be some relation to word categorisations and the actual room itself.

If there is a easy, intermediate and hard classification of words, my guess would be that the difficulty of words is weighted amongst the difficulty of the room. For example, in an Easy room, most words would be of the easy category with perhaps a select few from the intermediate category, because some words are slightly more difficult to draw.

Although saying that, in a user-created room, room operators can select the difficulty between 2 and 6 meaning that there could be 5 difficulty categories.
Edit: I don't think it would be related to how well people guess because everyone has a varying artistic ability.

Anyway, what I've said is purely a guess, I have no idea what actually goes on with wordlists. I think Feedback are the ones to ask for that :)

Well, if there is 2-6 to choose from, this probably means that some other input is added to the difficulty level...

There could be, or it could just be a selection from easy, intermediate and difficult, like the old options for Easy, "Normal" and Expert lists from a user-created room. It would be interesting to find out though.

Is there noone from feedback on this forum?

I don't think so, Feedback is a separate thing as far as I know. Although Betsy Shaver from Feedback is usually quite helpful. She helped me with my three wordlist submissions :)

I think the words are randomly selected for each game though I don't actually know. I think the only rule is that you cannot have the same word twice in each game.

As for why some words seem to come up more, maybe that's just down to your perception of the game. Possibly certain words stick out in your mind for some reason and you just don't notice the others as often. Maybe it's just chance that some words occur more frequently while you are playing. I know there have been occasions where I think a word is new to a word list and ask but everyone else has seen it many times. It's difficult to say without hard evidence.

Hmmm. I have kind of noticed this too. Coupled with the fact that there is difficulty 2-6 available makes me think that it could look something like this.

English Easy -
Difficulty 2-.5 probability
Difficulty 3-.3 probability
Difficulty 4-.2 probability
Difficulty 5-0 probability
Difficulty 6-0 probability

English Expert
Difficulty 2-0 probability
Difficulty 3-.1 probability
Difficulty 4-.2 probability
Difficulty 5-.3 probability
Difficulty 6-.4 probability

And then randomly selecting the word from the difficulty list after using the weighted probability to select which list to use.
Just a guess though