Which technique for gathering data (observational study or experiment) do you think was used in the following studies? Explain your answer. (a) The U.S. Census Bureau tracks population age. In 1900, the percentage of the population that was 15 years old or younger was 44.4%. In 1930, the percentage was 30,8% in 1970, the percentage was 17 9 and in 2000, the percentage in the age group was down to 28.5% (The First Measured Century, T. Caplow, L. Hicks, B. J. Wattenberg)

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