Standardized tests have been developed by commercial companies and evaluated through the use of a carefully chosen group of test-takers that represents a wide-range of "typical" test takers that are expected to use the test.
Results are statistically "manipulated" to find "average" scores (the "norm") for specific sections of the test. Test administration conditions are carefully controlled or standardized to ensure that each time the test is given, results will accurately demonstrate how the test taker has performed when compared to the "norm" group.
valid – the tests should be accurately testing the content that they are supposed to test
Use of a standardized test permits a valid comparison among scores from other tests that also are "standardized."
Criterion-referenced tests are scored according to a predetermined ABSOLUTE standard based on decisions by the test maker.