When Mitt Romney gave his convention speech on Thursday, as far as we can tell the collective response from the everyone in the country was, "Meh." I haven't seen any Democrats who said it was a disaster, but I also haven't seen any Republicans who said it was fantastic. And lo and behold, Gallup reports that 40 percent of respondents in their poll said Romney's speech made them more likely to vote for him, while 38 percent said it made them less likely to vote for him. That net positive of +2 makes Romney's the least effective speech since Gallup started asking this question in 1984. That's probably partly because the speech was nothing special, and partly because people are largely going to react along partisan lines no matter what it actually contained.
But one thing that's weird about this is that 78 percent of people expressed an opinion about Romney's speech. And in a separate question, a nearly identical 76 percent said they had watched at least some of the Republican convention. If that were actually true, it would have been the highest-rated convention in history. But of course, it isn't.
People regularly misreport their media use to pollsters, for any number of reasons. But in a case like this, the big culprit is "social desirability bias," in which people give the answer they know they're supposed to give. And if we believe Nielsen ratings—an imperfect system, but a whole lot more precise than a poll asking for self-reports of behavior—the ratings for the convention are a whole lot lower.
How much lower? Romney's speech garnered 30.3 million viewers, which is certainly more people than you'd want to have on your lawn, but a relatively small number compared to the size of the electorate. The adult population of the United States is around 240 million, which means that about one out of every eight potential voters actually saw Romney's speech. So two-thirds of us are willing to render a judgment on something we didn't actually see (although it's true that some people could be responding to press coverage they saw afterward).
And how does this compare to previous years? The answer is that while this year's Republican convention wasn't the least-watched ever, it was pretty close. Here's a chart, made using these data:
As you can see, a steady decline began in 1984, around the time cable television started to spread, giving people more viewing options and fragmenting the TV audience. The lowest-rated convention ever was the 2000 RNC, which averaged a rating of 13.9 (ratings represent the percentage of households with televisions watching that program). Why the 1976 GOP convention was such a hit, I'm not sure; maybe people tuned in to see if every one of the thousands of delegates would plunge a knife into a sleeping Richard Nixon in a political version of Murder on the Orient Express. In any case, chances are that the Democratic convention this week will get slightly higher ratings than Romney's, but nothing like they used to be back in the day.