In the United States, there's a widespread belief that statistics don't lie. Perhaps that's why surveys are such an important part of American life. For many years, politicians, businesspeople, and scholars have used surveys to find out more about that mysterious and complicated creature, the human being. American newspapers and magazines have been taking public opinion polls since the 1800s. In the 1930s, poll experts such as Elmo Poper and George Gallup began using scientific methods to select and interview participants in political surveys. Since the 1940s, American businesspeople have been developing, naming, packaging, and promoting products with the help of surveys. And also since the 1940s,surveys have been a major research tool among scholars in the social sciences. Psychologists and sociologists have asked people about everything from their religious beliefs to their sexual behavior. The mass media have frequently reported the results of these surveys, and the American public has always been quite interested in the responses. However, the most complete and most important survey for Americans is the national census. A census is the official count of the number of people living in a city, state, or country. The idea of a census has existed for more than two thousand years. In ancient Rome, the government counted its citizens for purposes of taxation and military service. But the first modern census began here in the United States in 1790. In that year, the population of the new nation was 3 929 214. Since 1790, the American government has taken a census every ten years, and the population has been growing steadily every decade. The 1980 census reported a population of 226 504 825. In addition to statistics on the total population, the 1980 census has given us a great deal of information about recent changes in American life. One of the many important changes concerns where people live. Americans are still a mainly urban people with about 75 percent of the population living in or near large cities. But, since 1970, the small communities have been gaining population at a faster rate then the cities or suburbs. American have been moving hack to the small towns and the rural areas. This is a dramatic change from the trend in preceding decades. Americans have always done a great deal of moving from one part of the country to enother, but, in recent years, the moves have been mostly to the South and West. States in the 'Sun Belt' have been gaining population, and states in the Northeast and the Midwest have been losing population. Marriage and family life have been changing, too. Americans have been marrying later, having fewer children, getting more divorces, and living more often as singles or as unmarried couples. The actual number of married couples has risen in recent years, but the percentage of married people has declined. Similarly, the number of actual births has gone up, but the size of the average family has gone down. The average young woman of today plans to have only two children. Along with many other surveys, the national census gives Americans a statistical picture of a changing society. It allows the government and the people to see what's happening and to adjust to the new picture. The main idea of the passage is that ______.