|Average hit points at level 3.|
An average of 7.5 versus the fighter's 13.5 hit points? Hardly a threat to anything but a lone kobold... Things get a bit more interesting at level 14 as the differences between the various classes become more pronounced (details):
|Average hit points at level 14.|
The thief has now moved past the halfling and the magic-user and is closing in on the elf. Of course an average of 32.5 versus the fighter's 50.5 is still not going to promote the thief into the front ranks. By the time we reach level 25, however, all of that changes (details):
|Average hit points at level 25.|
Now the thief is second only to the fighter having passed all the other characters on average. Only lucky dwarves could conceivably have more hit points than the thief now. This situation only solidifies by the time we get to level 36 of course (details):
|Average hit points at level 36.|
At this point the role of the "backup fighter" has clearly shifted from the cleric to the thief, as long as we ignore armor class anyway. So thieves, while starting out at the bottom of the hit point food chain end up close to the top of it. I found that surprising enough to put together a post with lots of nice graphs for you.
Addendum: Just for kicks, how does B/X compare to AD&D for the core classes? Not surprisingly, AD&D characters at level 20 are quite a bit more hardy than B/X characters (details):
|Average hit points at level 20 in B/X and AD&D.|
The B/X fighter lines up perfectly with the AD&D cleric and the B/X thief is way behind the AD&D thief. Even the AD&D magic-user, getting to roll until level 11, is slightly more beefy than the B/X magic-user.