Table 2.2 shows the result of the 2012 Presidential election and the predictions of several organizations in the days before the election. The sample sizes were typically about 2000. (The percentages for each poll do not sum to 100 because of voters reporting as undecided or favoring another candidate.)

(a) What factors cause the results to vary somewhat among organizations?

(b) Identify the sampling error for the Gallup Poll.

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TABLE 2.2 Poll Predicted Vote Obama Romney Gallup CNN/Opinion Research 49 50 49 49 ABC/Washington Post 50 47 Rasmussen Reports 48 49 NBC/Wall Street Journal 48 47 Pew Research 50 47 Actual vote 51.1 47.2