To make generalizations about a population, statistical information is taken from a representative sample. Every sample drawn from the population has its own statistic (, s, or r), which is used to estimate the parameter (μ, σ, or p) of its population. According to Fisher, a sample statistic should be an unbiased estimator of the corresponding population parameter. (Fisher created three other estimators for parameters, which had to be statistically consistent, efficient and sufficient.)
