This paper identifies and describes the primary sources of survey error in mail surveys and some methods typically used to assess and quantify some of these sources of error. Four sources of survey error- sampling error, non coverage error, non-response error and measurement error were discussed. Descriptions of how each of these sources of error occurs in mail surveys are provided. The paper summarizes ways of reducing these errors, if they cannot be totally avoided. Keyword: survey error, sampling error, non-coverage error, non-response error, measurement error, true score model
