Background : External quality assessment referred to the survey of different laboratories' results of a unique specimen as compared with a reliable reference. These assessments have been introduced since 1988 in Iran . Results were processed according to techniques of measurement and their accuracy was checked against the reference value.

Methods : We have gathered results of 14 parameters in 9 courses of external quality assessment, then compare the mean of each course with the expected value using paired t-test.

Results : Results have revealed the coincidence of measured parameters with expected results.

Conclusion : Despite the empirical nature of consensus hypothesis, it is revealed to be true in external quality assessment, thus it can be used to calculate the target value.