A sample is that part of a population which is actually observed. In normal scientific practice, we demand that it be selected in such a way as to avoid presenting a biased view of the population. If statistical inference is to be used, there must be a way of assigning known probabilities of selection to each sample. If the probabilities of different samples are all equal, for example, the method is called simple random sampling.
... Humboldt, (1769-1859), explored Central and South America, visited Siberia
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Helge Ingstad, (1899-2001), Norwegian, Danish explorer, Governor of Greenland
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Louis ...