= Statistical population
A <statistical population> is the collection of units, outcomes or distributional cases about which an analysis seeks conclusions. A finite population may consist of $N$ fixed values $y_1,\ldots,y_N$, with <population mean> $\mu_N=N^{-1}\sum_i y_i$. A superpopulation model instead describes observations through a <probability distribution>.
These viewpoints support different sources of randomness. In sampling from a fixed finite population, selection is random even if each value is fixed. Under simple random sampling without replacement, every unit has <inclusion probability> $n/N$, and the <sample mean> is unbiased for $\mu_N$. The accessible sampling frame can differ from the target population, producing a coverage problem that a large sample alone cannot repair.
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