Now let's go back to our Arena simulator (link1, link2), which runs combats for a several thousand dueling fighters as per slightly smoothed-out classic D&D rules, and compare. For this investigation I've done a few things. One: I've modified the simulator to start the combatants at 0-level (Normal Man), with a 1,000-XP requirement to reach 1st (Veteran). Two: I'll only look at the Man-vs-Monster duels, following the Monster Determination and Level of Monster Matrix in OD&D Vol-3, p. 10. Three: I'll end the analysis at character level 9 (Lord), because after that point the XP charts switch to a linear progression, which would not be following the same regression function as the levels up to that point. With a constantly-refreshed population of 10,000 fighters, after 200 cycles of combat this is what we get:
That table tells a scary story! Practically no one survives past the 3rd level. In this case, one lucky soul is still alive at 8th level. But there are no characters of Name level or higher in this population. Only 1 in 20 of this population is above the 0-level. While the OD&D description for Men says that every 50th man is 4th or 5th level, there are no such lieutenants or subalterns in existence in this group.
Keep in mind that this simulation is actually more forgiving than by-the-book OD&D, because I didn't implement any special abilities: no monsters with poison, paralysis, petrification, spells, blood drain, energy drain, charming, hit only by magic, etc. If we had included those surely the death toll would be even higher. Also: There's no aging-out, so that 8th-level survivor might be effectively a hundred years old or more. Let's compare the two populations side-by-side: on the left, the text descriptions that I'll call the "OD&D NPC Demographics", and on the right, the output of the Arena combat simulation using Vol-3 monster encounters, which I'll call the "OD&D PC Demographics".
Major conclusion: These populations are not playing the same game. They're not even remotely close; it's hopeless to even think about harmonizing them as-is. While the NPC population has a regressed level decay rate of about k = -0.60, the PC survivors from the Vol-3 monster encounters have a decay rate of almost twice that, over k = -1.00. Obviously if the first population has about 1-in-100 Name level leaders, and the second has none, then they are essentially contradictory.
This is not tremendously unique news, because we've pointed out in the past that the OD&D Vol-3 wandering monster tables are really far too tough (1st level characters have a 1-in-6 chance per encounter of a 4th-level monster like wraiths, gargoyles, lycanthropes, etc.) All later editions toned down those tables -- especially Gygax in AD&D, who arguably made the tables in the DMG too easy.
How can we interpret this for D&D? Perhaps we can best assert that, whatever the exact encounter tables, our PC's are playing "the most dangerous game", a much riskier and more desperate gamble in the dungeons and wilderness, where they might quickly win fame and fortune, but is most likely to end in hideous death. On the other hand, we can propose that our NPCs are following some entirely distinct path: a slower and steadier progression in experience among the army legions, guild halls, and colleges of magic. This latter progression is not so likely to result in death, but characters of a given level are likely to be much older than PC's of the same level. PC's will be gaining levels in just a year or so that NPC's take an entire life's career to obtain. We are reminded of Gygax's note on experience from AD&D DMG p. 85:
Note: Players who balk at equating gold pieces to experience points should be gently but firmly reminded that in a game certain compromises must be made. While it is more "realistic" for clerics to study holy writings, pray, chant, practice self-discipline, etc. to gain experience, it would not make a playable game roll along. Similarly, fighters should be exercising, riding, smiting pelts, tilting at the lists, and engaging in weapons practice of various sorts to gain real expertise (experience); magic-users should be deciphering old scrolls, searching ancient tomes, experimenting alchemically, and so forth; while thieves should spend their off-hours honing their skills, "casing" various buildings, watching potential victims, and carefully planning their next "job". All very realistic but conducive to non-game boredom!
Now, let's think about exactly how how far we'd have to bend the encounter tables in Vol-3 to create a PC population that resembles the distribution of the NPC population. What I usually do here as a zero-degree house rule is to modify the d6 on those tables (which determine level of encounter) by some subtracted number (minimum 1 in all cases). For example: with a -1 modifier the 0- or 1st-level characters cannot ever run into 4th-level monsters, at least. This modification bottoms out at a level of -5, which is equivalent to simply always taking a roll of "1" on those tables. Let's re-run the Arena simulator, again with 0-level entrant to the Arena, for each of those modified levels:
The best fit to our NPC population is the "Mod -4" table (most but not all encounters being at the minimum level possible on those Vol-3 tables), with a decay rate of k = -0.58. We might say that this much safer game is equivalent to what the NPCs in our campaign world are playing at.
As I've said before, in my own games I do modify the rolls on those encounter tables downward in a fashion similar to this. On the one hand, I wouldn't actually use the -4 modifier; that's both too repetitive and doesn't honor the higher-variance game that the PC's have chosen. At the moment I'm splitting the difference in half: applying a -2 modifier to those encounter level rolls, and it's feeling about right. The encounters now only ever vary from the PC/dungeon level by a maximum of ±1 level; but on a 6-level monster level scale as in OD&D, that still covers half of all the monsters in the book.
Further research required: Propose a system for assessing the XP gains by NPC characters, who are pursuing safer and more "professional" advancement than the dungeon-delving PCs.
Next time: A comprehensive system for establishing high-level character ability scores.