>>The gradual increase in play time over the levels might be due to several factors:
Or the shift in focus to earning credits rather than xp. It was true for me, and true for all my friends that play. Mounts happen at 40. How could you failt to take this into account?

One reason for the high number of level 1 characters is the use of the mule. Posting items to an alt character for either auction or just to hold on to.

Other factors that could be causing an increase in play time as level increases:

1) More time is required to achieve goals.
I reached lvl 5 and completed many quests within the first 30-45mins of play. At lvl 20 it takes 3-4hours to reach lvl 21 this is due to the larger xp requirement but also because your time is now divided between professions, auction house runs, more challenging quests/dungeons which mean more deaths and therefore more downtime. Also there is more need to find a good party to group with which in itself can take time.

2) The game becomes addictive. The more you play the more important it becomes. It starts of as just another game but then you find you wake up early (e.g. 5am) to get a couple of hours in before work and you justify this because you desperately needed to get skill X or you were so close to achieving significant goal Y.

3) The game is paced in such a way as to give you more and more to do as your lvl increases. As already mentioned your time gets divided more and more as there are more things to do. At lvl 1 you are not going to be worried about maintaining your honor (PvP servers) but at lvl20+ this is becomes more and more important. As do professions and auction houses and mounts etc. Higher level more to do, more fun, more play time.

Play time and travel time appear to correlate as the level rises. Would posit that the amount of "active" play remains the same with the increasing travel time being a factor in the gradual rise.

Above posters and original data all make good points. The amount of play time required to accomplish a level increases dramatically over time. Those that cannot put in that amount of time (whether by choice or not) will take much longer to level, a statement that produces and represents this graph. The graph as such doesn't represent anything particularly remarkable, particularly since all players strive for 40 to get the mount, because the 0-ending levels "feel like" milestones, and because the 0-ending levels often ARE milestones in terms of character abilities. Hunters get Aspect of the Pack at L30, for example.

An interesting datapoint that's not here is Tradeskills. Tradeskills in WoW are level capped as well as many other things ( like the mounts ). The level requirements are as follows:

Apprentice requires level 5
Journeyman level 10
Expert level 20
Artisan requires level 35

The spike you're seeing at 40 is, no doubt, what others are saying: you get your mount ( horse, cat, beast, what have you ) at 40 and thus a huge movement increase. This is a game-defining change in WoW since, while there are many modes of travel in WoW, there are very few that will get you from any random point to another random point quickly. Flightmaster are only defined points, and Zepplins the same. Mages and Warlocks can teleport and summon respectively, but it's limited ( or requires help of other characters ). The mounti s a major change in playstyle.

Tradeskills are the ability to create items of all kinds ( armor, weapons, food, etc ). Gaining in skill is trivial, the system allows you to complete multiple combines ( and multiple skill increases ) with a single mouse click. However, the amount you can increase is limited by the level of your character, as noted above. The fact that we do NOT see corresponding level spikes at those levels tells us that tradeskills, while being interesting and apparently heavily used in game, are not a driving force for players and character advancement.

While this may not seems terribly interesting, it does speak about the usefullness of the tradeskilled items in game. It may also say something about players and thier willingness to advance thier characters along a "non-agressive" play route rather than the standard "agressive" experience advancement route ( tradeskills generate no level-related experience ). Although, I lean more to the former than the latter, since I myself an a tradeskill player, and I can see that the items produced, by and large, have little impact on gameplay.

A similar study would be interesting in other games, to compare players willingness to participate in virtual, non-aggressive playstyles. If the rewards of tradeskills more matched the rewards of level advancement, it would be very interesting to examine MMORPG socio-dynamics from that data.

Excellent point, Thoreac. What's funny is to look at the reasoning behind the decision - presumably it is to limit the development of alts specifically for crafting. In DAoC, for example, many people created characters that they NEVER levelled, explicitly for crafting. People had an "alchemy alt," for example.

I ask the question because I am actively wondering what kind of behavior they were trying to prevent or encourage. I'm guessing that they wanted tradeskills to be as closely tied to the game and to the characters as anything else, and so implemented the level requirements, but it is interesting that what you say is likewise true: tradeskills do not have sufficient impact on gameplay as a whole. It's as if they created the level requirements and then failed to do anything else to build the relationship of the tradeskills and trade products into the game itself.

I find the level limits for the tradeskills very low for a non-alt character. That is, a level 34 character has little chance of acquiring the materials by himself necessary to train up to an artisan skill (except through arbitrage and then buying materials at the AH [Auction House]).

Now that I think about it, there seems to be an intended correlation between adventuring (questing and grinding), tradeskills, and the AH. You can solely adventure and reach level 60. But you soon discover that your collected savings can buy useful items at the AH. And that you can sell items (wool cloth being the prime example) for much higher prices at the AH than a vendor. Picking up a tradeskill further educates you about the operations of the AH, as you learn which items are needed for tradeskill materials, and how their prices vary. Judicious use of tradeskills makes you a few items for personal adventuring use, and many more items for selling at the AH, or for donating to fellow guild members. But guild dynamics are for another post entirely. :)

A few levels before 40, people begin to grind cash for their mounts. 90 gold isn't easy to come up with and many, like myself, find a good cash location and grind away. This is slower leveling, and hence the reason for higher play times from 37-40.

PvP brackets may be another factor in seeing more playing time just before the next multiple of 10. Players who spend a lot time running battlegrounds are likely to spend a lot of time holding at x9 before moving to the next level bracket.