The IQ test is the best known example of norm-referenced assessment. Many entrance tests (to prestigious schools or universities) are norm-referenced, permitting a fixed proportion of students to pass ("passing" in this context means being accepted into the school or university rather than an explicit level of ability). This means that standards may vary from year to year, depending on the quality of the cohort; criterion-referenced assessment does not vary from year to year (unless the criteria change).[15] Ipsative assessment is self comparison either in the same domain over time, or comparative to other domains within the same student.