"You’ve heard of the “margin of error” in polling. Just about every article on a new poll dutifully notes that the margin of error due to sampling is plus or minus three or four percentage points. But the “margin of sampling error” doesn't even come close to capturing the potential for error in surveys. Polling results rely as much on the judgments of pollsters as on the science of survey methodology.... pollsters make a series of decisions when designing their survey, from determining likely voters to adjusting their respondents to match the demographics of the electorate. These decisions are hard. They usually take place behind the scenes, and they can make a huge difference. To illustrate this, we decided to conduct a little experiment:We decided to share our raw data with four well-respected pollsters and asked them to estimate the result of the poll themselves..."