Random error refers to the fact that any survey measure taken over and over again may well be different (by some small amount) upon each measure, merely due to chance measurement imprecision. Thus, compared to the true value of the measure for a given respondent, the observed value will be on the high side some of the time and on the low side other times. This deviation of the observed value from the true value often is signified by e in the following formula:
X=T + e,
where X is the observed value and T is the true value. In theory, over many similar measures of the same variable taken from the same respondent, the average of the observed values will equal the true value. That is, ...
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