These lessons should make us less sanguine about the potential use of sampling for the official 2000 US Census. Right up to Election Day, major national polls had President Bill Clinton ahead of Senator Robert Dole by double digit percentage point leads. Most major polls radically erred and predicted election results far outside the stated margins of error. One major poll consistently found much smaller differences between support for Clinton and Dole, the Zogby poll by John Zogby. The table below shows the major poll predictions and the actual election outcome.
Values are in percentage.
The stated margins of error were only a few percent. The reason is because the quoted margin of error, the sampling or random error, is just one error source. All the polls suffered from about the same level of sampling error, but they labored under different levels of systematic error. Given a finite, randomly selected sample of a population, the size of the sample determines how well that sample can characterize the population. These statistics are well understood.