First, there are 292 self-answered questions on the site out of 3960 for 7.37% of all questions.
There are 116 self-answered questions where the answer was posted immediately after the question for 2.92% of all questions by 39 users for 0.4 % of all users.
The way I can tell that the poster answered immediately is that the Post.Id of the answer is exactly one more than that of the question.
To compare the quality of the immediate self-answer to the averages for all questions.
Answer Score Average
Overall -> 7.17
Self -> 10.51
Question Score Average
Overall -> 10.34
Self -> 10.41
Average Number of Views
Overall -> 2514.71
Self -> 2442.5
Average Number of Favorites
Overall -> 1.94
Self -> 3.10
Average Number Answers
Overall -> 2.44
Self -> 2.28
As you can see, the only metric in which the self-answers are lower is that of views and the answers are on average significantly better.
The number of answers attracted by a self-answer is lower, which is better because if someone writes a definite answer that covers all of the bases, then other people are much less likely to answer.
The other thing worth mentioning is the type of users who immediately self answer.
Average Reputation
- Overall -> 154
- Self -> 7677.79
- Percentage of Total -> 19.76
Average Number of Votes Cast
- Overall -> 12
- Self -> 1284.90
- Percentage of Total -> 42.04
Average Number of Badges Gained
- Overall -> 4
- Self -> 94.38
- Percentage of Total -> 14.79
I hope that I am making my points really clear here,
Questions that are answered immediately after asking are just as good on average as questions that are not and on average have better scoring answers.
The users who invest the time to write both the questions and answers are among the best and most involved on the site (0.4% of the users doing 42% of the voting) and we should be encouraging the them to keep posting.
If the self-answers weren't asking real questions, I think the community would have caught on by now, and if they were doing it out of selfishness, they probably wouldn't be as involved with the voting/flagging/editing as they are.