This question on cellphones and cancer was recently asked. Now it's clearly a duplicate of this question, which was very well answered and accepted, and ordinarily the new one should be closed as a duplicate. The only problem is that the previous question is months old, and significant new information has been made available since then. Essentially the old answer is not really correct.
So how do we make sure that the best information is provided to our readers? It makes no sense to have two active and identical questions with different answers. It's going to be hard to get a new answer to the old question upvoted enough to displace the old one.
- Close the old question as a duplicate of the new, and let a new good answer arise
- Let both run for a while, and then close the old if the new one ends up with a better answer
- Encourage people to downvote the old incorrect answer.