单项选择题

TEXT A
The first pre-election poll, or straw vote, as it was then called, was conducted by the Harris bury Pennsylvanian before the 1824 presidential election. This straw vote and the many that followed it really registered nothing but local opinion; however, as communications improved and elections were won by closer and closer margins, newspapers and journals tried desperately to satisfy their readers’ curiosity in more reliable ways.
Before the 1928 elections, no fewer than 85 publications made private inquires, generally by means of questionnaires sent to subscribers and by telephone surveys. The principle common to all these inquiries was that they depended on quantity rather than quality; little effort was made to reach representatives of all segments of the population. Still, the erroneous belief persisted that the greater the number of questionnaires, the more accurate the results would be. The record was held by the American monthly Literary Digest, which sent out millions of postcards with short and pointed questions before each election and received many hundreds of thousands of replies. In fact, in 1932, the Literary Digest’s forecast was off by only 1%.
In view of such striking achievements, it seemed rather impertinent for the young American journalist, George Gallup, to claim that large numbers were irrelevant and that equally accurate or better predictions could be made with a small but carefully selected sample of the population and a small team of skilled interviewers.
In 1936, it took Gallup a long time to convince 35 newspaper editors that his system was much cheaper than the customary mass inquiries and that it could provide surprisingly accurate predictions. The editors finally agreed, on condition that if Gallup’s predictions were less accurate than those obtained by the tried method of the Literary Digest, he would have to refund the entire cost of the investigation. Although the Literary Digest broke its own record by obtaining 2 million replies to its electoral postcards that year, its prediction was wrong by 19%, whereas Gallup’s was off .by less than 1%.
Moreover, the Digest had predicted that Alfred M. Landon, the Republican candidate would obtain 56% of the votes cast, whereas Franklin D. Roosevelt was, in fact, re-elected with an unusually large majority. Gallup was one of the few political prophets who predicted this result.
Suddenly Gallup’s name was on everyone’s lips, not only was he the prophet of the moment, but it was generally conceded that he had found a new and most important scientific method of prediction. He was showered with money and commissions, and the Gallup Poll became a generic term for public opinion polls.
Unlike earlier prophets, Gallup based his investigations on sociological rather than purely arithmetical calculations. He realised that the electorate is made up of different social strata with differing political trends. Thus, farmers do not vote in the same way that industrial workers do, the North votes quite unlike the South, Black preferences vary from those of White persons, the interests of employers are different from those of employees, and so on. There are also voting differences according to age and sex, for it appeared that older people and women tend to vote for conservative parties.
Gallup usually sampled his subjects according to six factors: state, size of community, age, sex, income, and political affiliation. From time to time, other factors may be considered; during times of war, for instance, the national origins of electors may be taken into account.
Only when the composition of the electorate has been accurately determined can the purely arithmetical question-how many people in each bracket must be interviewed-be solved. Once this is done, laws of probabilities take over and the more people interviewed, the more exact the estimates will be. However, above a certain maximum number of interviews, the accuracy increases by no more than a fractional percentage and where errors of up to 2% are permissible, a few thousand questionnaires will accurately reflect the opinion of the total US electorate.
It is true that not all Gallup’s predictions were as accurate as that, for of the 114 election forecasts made by the American Institute of Public Opinion between 1936 and 1944, only 19 were wrong by less than 1%; 39 were off by between 2% and 3%; nearly half were off by more than 3%, and 6 were off by as much as 10% to 15%. The Gallup method suffered its greatest setback during the 1948 presidential election when Truman-not Gallup’s choice, Dewey--was elected. Before Eisenhower’s election in 1952 and re election in 1956 there was less doubt about the outcome, and Gallup did, in fact make fairly accurate predictions.
The American results have been excelled by those obtained by Gallup’s British Institute of Public Opinion, which, using the same methods, has managed to forecast a number of parliamentary elections with a margin of error of only one half of 1% . In France, too, the French Institute of Public Opinion has managed to predict parliamentary results with a margin of error that has rarely exceeded 2%.
After his more than 20 years’ experience with surveys, it would be fair to say the Gallup’s method of sampling the electorate has proved most successful. Before Gallup, political predictions were no more than shots in the dark, and it is as a result of his achievement that today we can make truly scientific forecasts in this difficult field.
Which of the following may be unnecessary in conducting Gallup Poll