I am confused about how to determine statistical significance in election polls. I was taught that overlapping confidence intervals do not necessarily imply a statistically insignificant difference between two values. I was Googling around for an answer, and this article confirming it.
However, this article seems to give a different interpretation. In particular, I'm concerned about a simple yes/no poll question (or Candidate A / Candidate B), and not in the case where there is a 3rd option. The claim the second article makes is that, in this simplified case, one can simply add the confidence intervals and if they overlap, then the difference is not statistically significant i.e Candidate A at 53% and Candidate B at 47% with a +/- 3% MOE is not statistically significant.
The two articles seem to be at odds and I would like to understand why. Is it because, in the case of yes/no polling, the two values are perfectly negatively correlated?