Donald Trump's victory in Tuesday's presidential election defied the projected outcomes put forth by numerous polls leading up to the event, which favored Democratic candidate Hillary Clinton. But why were the pollsters so far off?
The underlying reason for this large-scale polling failure — which is evidenced by the missed preferences of a significant portion of the American electorate — is low response rates, according to the Harvard Business Review.
Caller ID is largely to blame. The ubiquitous use of caller ID technology means fewer Americans answer the phone when a pollster calls, meaning it takes more calls for a poll to reach enough respondents to create a valid sample size. The ability to collect data has declined, and if inputs are bad, so is the analysis, according to the report.
Screening calls with caller ID and ignoring pollsters is problematic also because it hinders the randomness of the sample population. While it's not problematic for people to ignore pollsters on the phone if they do so for random reasons, it is a problem if people of similar interests, characteristics and demographics all exemplify similar behavior when it comes to participating in the polls.
Response rates to modern telephone polls are below 15 percent, according to the report, making it harder to know whether people are excluding themselves from the polls for reasons associated with the outcome the poll seeks to measure.
It's also difficult for election pollsters to determine who is actually going to vote on Election Day. People tend to say they plan on voting even when they won't, so it's necessary to ask additional questions, such as interest in the election, past vote behavior and knowledge of where a polling place is, according to the report.
It also may be the case that standard sampling and weighting techniques fail when the polls miss facets of the electorate that are likely to vote in a given election but haven't in previous ones. A group that generally doesn't vote is also less likely to respond to a survey on the election, according to the report.