50 percent of likely Democratic primary voters support Clinton as their choice for the party's nominee, with 48 percent backing Obama.But taking into account the poll's sampling error of plus or minus 4½ percentage points for Democratic respondents, the race is a virtual tie.
First of all, I'm going to put aside the fact that if the sampling and polling techniques are not done properly than any poll tells us absolutely nothing (since it conveys information only about the sample and not about the entire population). Anyone who knows anything about polls knows this, of course. But the press never mentions it at all, and over the years I have discovered through my students that many readers of press coverage on polls therefore have no idea that a poll could ever be more wrong that the sampling error. (OK, I didn't put aside that fact.)
Let's assume, however, that this poll was properly conducted. Does it tell us that Obama and Clnton are tied? What, for that matter, is a virtual tie? Read straightforwardly the poll tells us that Clinton's support lies somewhere in the range between 45.5% and 54.5%; Obama's support lies somewhere in the range between 43.5% and 52.5%. Therefore, it is true that they could be tied. It is also true that either one could be ahead of the other slightly. Moreover:
- Clinton might be ahead by 11 points
- Obama might be ahead by 7 points
Is that a tie, or a virtual tie? No.
I think what the reporter means to say is that the poll cannot indicate clearly whether either candidate is ahead. Saying that they are in a virtual tie is like... (this analogy took me a while to come up with, and may not work, so bear with me)...the following:
The score in the football game is 7 to 10.
I hear a news report that one team has just scored, but I don't know which team.
So, assuming no safeties or missed extra points, the score could be
- 14 to 10
- 10 to 10
- 7 to 13
- 7 to 17
Let me just close in noting that this is a ridiculous subject for me to blog about. I'm guessing there are about 5 readers of SecondAmericano: 3 of them know far more about politics and polling than I do, and one of them knows far more about statistics than I do. Still, if you can't preach to the choir, then what good is preaching (and besides, if I screwed something up here, I'm sure to be quickly informed).