What is a Sample(statistics)?
Very often it is not possible to study the entire population – it may turn out to be very expensive and also time consuming. It may take such a long time that the data might become obsolete. Hence a sample which is representative of the population is studied. Sample is that part of a population which is actually observed. In normal scientific practice, we demand that it is 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. In mathematical terms, given a random variable X with distribution F, a sample of length n\in\mathbb{N} is a set of n independent, identically distributed (iid) random variables with distribution F. It concretely represents n experiments in which we measure the same quantity.
