Question:

A New York Times/CBS News poll asked the question “Do you favor an amendment to the Constitution that would permit organized prayer in public schools?” Sixty-six percent of the sample answered “Yes.” The article describing the poll says that it “is based on telephone interview conducted from Sept. 13 to Sept. 18 with 1664 adults around the United States, excluding Alaska and Hawaii….the telephone numbers were formed by random digits, thus permitting access to both listed and unlisted residential numbers.” The article gives the margin of error as 3 percentage points. Opinion polls customarily announce margins of error for 95% confidence, so we are 95% confident that the percent of all adults who favor prayer in the schools lies in the interval 66% ± 3%.

The new article goes on to say: “the theoretical errors do not take into account a margin of additional error resulting from the various practical difficulties in taking any survey of public opinion.” List some of the “practical difficulties” that may cause errors in addition to the ± 3% margin of error. Pay particular attention to the news article’s description of the sampling method.