(symbol: SE) a quantification of the inherent inaccuracy of a calculated population value that is attributable to random fluctuations within the sample data upon which it is based. It is expressed as the standard deviation of the sampling distribution. For example, the sample mean is the usual estimator of a population mean, yet different samples drawn from that same population will yield different values for the mean. Thus, to determine how much sample variability exists, the standard error of the mean may be obtained by taking the standard deviation of all of the means over all of the samples taken. Standard error is expressed in units given in the same scale of measurement that was used for the sample data (e.g., for a set of means that are given in weight the standard error unit is also a weight).