The difference between the observed values of a variable and the long-run average of the observed values in repetitions of the measurement is (the):

Errors: Error that results from chance variation. Differences in the results between the population of interest and the sample. These errors occur because you cannot interview each and every person in the population of interest (that would be a census rather than a sample). It can also be defined as the difference between the observed value of a variable and the long run average of the observed values of that variable in repetitions of the measurement. Random error is also referred to as sampling error or random sampling error (not to be confused with sample design error). Random error can be reduced by increasing the sample size.