#sample_distribution__sample  items selected from a population and used to test hypotheses about the population
  supertype:  #statistical_distribution__statisticaldistribution__distribution  an arrangement of values of a variable showing their observed or theoretical frequency of occurrence
  subtype:  #random_sample  a sample in which every element in the population has an equal chance of being selected
  subtype:  #stratified_sample__representative_sample__proportional_sample  the population is divided into strata and a random sample is taken from each stratum

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