population parameter

a parameter, or numerical feature, of a population of scores. Usually refers to either the mean or variance of a population.

Often it is important to know about the entire population that is being investigated or researched. For instance, if a researcher is studying blood pressure, it is useful to know what the mean blood pressure is across the entire population, and what the variance is as well.

Similarly, when studying child development, it is useful to know what developmental milestones are reached at what ages.

Population parameters can usually not be known directly. Instead, they are estimated from a sample of the population.