... at a guess I'd say that the *average party level* within a game goes up by maybe 1-2 levels a year ...
Now I'm thinking about it, though, I suppose I have to run some numbers. This might take a while...
Well, that didn't take as long as I thought it would.
I can post the specific data here if anyone likes, but here's the generalities:
Preamble: all games are 1e-based, with no ExP given for treasure (thus a slower-than-designed advancement rate). All games start at raw 1st level. I have a sample size of 6 campaigns over 28 years: 3 big ones that got to 10th-ish level, one smaller one that finished at around 5th-6th, and two new ones. All levels refer to the approximate average of the party or parties; individual characters can and do vary wildly from these at any given point.
Year 1: All campaigns except one either stay at 1st or poke their nose into 2nd. The one exception is a new one where advancement was sped up, it got to 4th in year 1.
Year 2: All campaigns get out of 1st; finishing at anywhere from 2nd to 5th. (one new campaign is still in year 2, with parties in the 3rd-5th range)
Year 3: All campaigns get out of 2nd, most are 4th-5th. (the other new campaign - the faster-advancing one - is still in year 3 and is around 6th at the moment)
Year 4: Range is 4th to 6th, except one disaster that went backwards from 4th to 2nd during the year! It would never recover from this, and by year 8 when it ended it still had not reached 6th level.
Years 5-8: The three big campaigns settle in to a 5th-8th range, with lots of ups and downs; except one party in one of the campaigns that stalled at 4th-5th, stayed there for 4 years, and never went further.
Years 9-10: Range is now 7th-9th for the three, again with ups and downs.
Years 11-12: The major parties from the two campaigns that got this far are in the 8th-10th range, with minor parties still as low as 6th in some cases.
Make of the above what you will. My point, perhaps, is that games do not need rapid level advancement to be long and successful.
Lanefan