Back in December, a SurveyUSA poll drew some attention and fueled the hype regarding the large crowds expected for Tuesday's inauguration ceremonies. In that poll, an incredible 12% of respondents reported that they were planning to "attend the inauguration of President Obama in Washington, DC." That would translate into over a half million Atlantans making the 500+ mile flight (600+ mile drive) to DC for the ceremony.
Of course, most of us probably know people who originally said that they were going to attend but later backed out for any number of reasons. But just during the past week, SurveyUSA asked adults in the New York and Los Angeles media markets whether they planned "to go to Washington for the inauguration." Remarkably, 9% of New Yorkers reported that they were planning such a trip while 6% of those in Los Angeles said the same. For some perspective, the adult population of the New York media market is nearly 16 million while the Los Angeles market has nearly over 12 million adults. Thus, if we took these polls at face value, DC would be expecting over 1.4 million visitors from New York and over 700,000 from Los Angeles. Are 2.1 million coming to the district from just these two markets? Not likely.
One problem with a question like this one may be that it lends itself to social desirability bias. As we know, citizens tend to over-report the extent to which they will (or did) vote in elections. In a similar way, some respondents may be proclaiming that they will attend the inauguration when they don't have any real intention of going. They may do so because they hear of so many others who are attending and they feel as though it is something they should be doing as well.
However, even if citizens gave honest answers to the question about whether they were going to attend the inauguration, surveys still wouldn't be a very useful instrument for generating crowd estimates. For instance, let's assume a national poll showed that 2% of American adults were attending the inauguration ceremonies. That would translate into approximately 4 million adults. However, even if you had a margin of error of just 2%, you would only be able to confidently say that the expected crowd may be anywhere between a few thousand (which would be the equivalent of a calm summer day in DC) to as many as 8 million (a number that would cripple the area's transportation infrastructure). Thus, polls such as these may provide a fun way of capturing excitement about the event, but they are not very useful for estimating how large the crowd will actually be.