Every election year, journalists have a feast over the hundreds of poll results that never seem to end. They frequently abuse language as they try to explain what the polls mean. Because polls are small samples of people, poll results can only say so much. Specifically, when races are tight, they don't tell us much. This lack of clarity creates a certain nervousness among the prognosticators.
It was refreshing to see this headline: "Among Republicans, Santorum in statistical dead heat with Romney". (link) When was the last time the news tell us two candidates are neck and neck? The actual result was 30% Santorum to 28% Romney. You'd expect a headline like "Santorum slightly in front of Romney", even though the difference between them is statistically meaningless.
Some other media called this a "virtual tie". I hate this term. A "virtue tie" is a tie that really isn't. Alternatively, a "virtual tie" is nearly a tie. Neither sense of the word is applicable here. It is a tie, nothing "virtual" about it. In fact, when the Washington Post prints "Polls show Rick Santorum virtually tied with Mitt Romney nationally" (link), it gives the impression that Mitt Romney is slightly ahead... that story certainly did not come from the Pew poll. By the way, the Post manages to print this article and mention two recent polls without actually citing any numbers!
I just have to re-print the following table from Pew's press release here. Reporters frequently ignore the margin of error (again, this Yahoo reporter did well to feature the margin of error in the 2nd paragraph). Because these are polls with very few respondents, the margin of error is plus/minus 5 percentage points or more (for any subgroup being analyzed).
The 30% to 28% comparison was made for respondents who are "Republican or leaning Republican registered voters". This means the margin of error is given by the fourth line up from the bottom, which is plus/minus 5 percentage points. This means that the poll can only tease apart differences of larger than 10 percentage points. Notice that for any result concerning Republican voters (excluding those who said they are leaning Republican), the margin of error is even larger, at plus/minus 6 percent.
Yes, if you think these polls are useless to measure tight races, you'd be right.