Items selected at random from a population and used to test hypotheses about the population
The null hypothesis attempts to show that no variation exists between variables, or that a single variable is no different than zero. It is presumed to be true until statistical evidence nullifies it for an alternative hypothesis.
Estimation of an unknown quantity between two known quantities historical data, or drawing conclusions about missing information from the available information.
Bias introduced to a sample when a large fraction of those sampled fails to respond.