A characteristic (or numerical quantity) of the distribution of a population or a distribution of scores such as the mean or standard deviation (i.e., measures of central tendency) as distinct from the property of a sample drawn from a population. Within a population, it is a fixed value that does not vary. While it is often used interchangeably with variable, this is incorrect as it differs in meaning. A variable is something that is open to manipulation by the experimenter. A parameter is independent of the variable and sample size.
See Parameter (linguistics), Population (biology and ecology), Variable