Let me start out by saying that James missed a HUGE part of AD&D expo in his article - loot. Expo for loot recovered is more than what players can expect in by the book AD&D, which kind of throws off his numbers - and hit point.
Read the article without my insightful observations at the WotC website.
By James Wyatt
I talked last week about the rate at which characters acquire magic items as they gain levels. So let's back up and talk about the rate at which characters gain levels! (lets back up even more - in AD&D 1e, characters gained expo from gaining magic items)
How Many Goblins . . .
I'm curious: How many goblins does a 1st-level fighter have to defeat to reach 2nd level?
In 1st and 2nd Edition AD&D, a goblin was worth around 15 XP. A fighter needed 2,000 XP to reach 2nd level. That's a lot of goblins—134 goblins would make the fighter 2nd level if you assume the fighter killed them all alone. (and completely discounting any loot that might have been recovered from said Goblins - the math is wrong right out of the gate)
In 3rd Edition D&D, a goblin was a CR ⅓ monster, so 3 of them were an appropriate challenge for four 1st-level characters. That means a 1st-level fighter would get 100 XP for defeating 1 goblin. All characters needed 1,000 XP to reach 2nd level, so 10 goblins would bring the fighter up a level. (alright, even taking into account loot in 1e, this really does show a change in the dynamics of leveling)
In 4th Edition, that goblin might be a level 1 minion or a level 1 lurker or skirmisher. If they're minions, each is worth 25 XP, so the fighter (who needed 1,000 XP to reach 2nd level) would need to defeat 40 goblins. If they're not minions, each is worth 100 XP, so the answer is the same as in 3rd Edition: 10 goblins to reach 2nd level. (is there really that much of a difference between 1st level minions and non-minions in 4e? they all die with one hit more or less)
That's a pretty random measure, but it certainly speaks to different expectations of level advancement in the different editions of the game, as well as some variable understandings of the threat presented by a single goblin.
How Many Encounters . . .
It's hard to judge what the pace of level advancement actually looked like in AD&D, for a couple of reasons. First, different characters advanced at different rates—the fighter needed 2,000 XP to reach 2nd level, but the thief needed only 1,250 XP and the magic-user needed 2,500. (it all balanced out as time went on) Second, there weren't any clear guidelines for what an appropriate encounter was. But a roll on the random monster tables for a 1st-level dungeon would yield an encounter worth, on average, about 90 XP. For a party of four characters, that's 23 XP each. So 87 of those encounters would bring the fighter to 2nd level! Any treasure found in those encounters would also contribute XP to that total, so the actual number of encounters could have been much less—possibly more like 40. (and don't forget treasure found outside of those encounters - and who rolled random encounters for ALL of the rooms in a 1e dungeon?)
Oy. I've said it before: I think one of the great advances brought to the game by 3rd Edition was a clear guideline for how to build an encounter to challenge a party. (I'm going to say it and I'm SURE there will be a large number that disagree, but that led to 3e's cookie cutter encounters for those that bothered with CL) And that guideline undergirded the math of character advancement. The charts were built so that a character would advance a level after 13⅓encounters of the same level. 4th Edition stayed on the same trajectory, but adjusted the expectation to about ten encounters—or eight encounters, one major quest, and one minor quest per character in the party. (I'm not much on formalistic adventure design - YMMV)
How Many Sessions . . .
There's psychology behind the question of level advancement. Games reward you for playing: An opponent lands Park Place where you have a hotel, and you collect a fat wad of cash. You play a 7-letter word on a triple word score and write down 180 points on the score sheet while gloating over your opponents. You beat your previous high score, end up on a leaderboard, or earn an achievement. You get a power-up, finish a level, or send your opponent flying off the screen. (these are games where you are playing against others, not with others. No so sure how the examples hold up)
The rewards in D&D include experience points (earned after every encounter), treasure (earned after some encounters), new class features (earned each level), and new feats, spell levels, ability score increases, and the like (earned at some new levels). You might earn treasure or XP as a reward for completing an adventure. Many DMs award XP after every game session rather than every encounter. 4th Edition gave action points at every milestone (every two encounters). (too many carrots - holy shit)
But you see what I'm getting at: rewards of different magnitude come at different intervals. That's good—our brains respond well to both small, frequent rewards and large, infrequent rewards, and a good game design offers both. Without frequent small rewards, players begin to feel like their efforts aren't paying off. They're doing a lot of work with nothing to show for it. Without occasional large rewards, encounters feel like pushing a button to get a morsel of food—a repetitive grind with no meaningful variation. (gotta love the imagery - if pushing a button to get a morsels of food is what game design comes down to these days, I'm glad I play games built on older rules systems)
So the trick to figuring out level advancement is figuring out how often players need that very significant reward. (here's the real trick - in a good campaign with a skilled DM and players looking to have fun, the fun is the carrot more than any other trick) A number of factors go into answering that question: How long does it take to get used to playing your character at a new level? How long do you want to play the character at that level once you're used to it? How big is the reward of going up a level? How do you ensure that players have a feeling of progress without feeling like they're getting rewarded for nothing? (overthinking... or maybe not. sometimes we don't want to know how the wizard behind the curtain does what he does, we just want the end results. when magic can be broken down by science, it is no longer magic. A good campaign is magical)
In 3rd Edition, 14 encounters would get you up a level, but how long did it take to complete those encounters? Of course, that depends: How long are your sessions and how often do you play? If you play four-hour sessions, how much do you get done in one session?
The 4th Edition DMG reveals some of the expectations that went into building the XP math for that game (an edition over done with the math behind the game to the point the magic was lost):
If you were to start a campaign with 1st-level characters on January 1st, play faithfully for four or five hours every week, and finish four encounters every session, your characters would enter the paragon tier during or after your session on June 24th, reach epic levels in December, and hit 30th level the next summer. Most campaigns don't move at this pace, however; you'll probably find that the natural rhythms of your campaign produce a slower rate of advancement that's easier to sustain.
At four encounters every weekly session, characters would reach a new level every other week, and we thought that felt about right. We also adjusted the scale so that you'd hit 2nd level pretty quickly—the first hit is free, so to speak. (nice! just like the crack dealers in the mid to late 90's in the South Bronx that I used to collar up. As if I didn't have enough reasons to dislike 4e already)
Where We're Heading
Our current design is going in a similar direction: advancing pretty quickly at low levels. It's a little tricky to nail it down, because our expectation of what an appropriate encounter is has changed somewhat. We expect every adventure to include a mix of easy, moderate, challenging, and really hard encounters (I so detest formulas). That said, a 1st-level character should hit 2nd level after about 6 moderately difficult encounters. (I'm not sure yet, but that might be 15 goblins' worth of XP.)
Compared to the previous two editions, an encounter can go much more quickly, so (again, depending on the length of your sessions) it's not unreasonable to think that you'll hit 2nd level after a single session. Another session might bring you to 3rd level, two more to 4th, and three more to 5th level. You might hit 20th level within a year of play, assuming a relatively steady rate of play. (i'm not going to say this is excessive or now, as I tend to enhance the expo the longer the time is between sessions - the more infrequent the sessions, the large the invisible expo bonus. Again, I don't like the formula, but that is my opinion. I have a successful blog, so my opinion must count more ;)