The district is considering changing the achievement tests that they administer. A new alternative test is much shorter and, if valid to measure student achievement, could save substantial instructional time. This year the school will administer both tests and assess the validity.

content validity                              

Explanation:

In simple words, The truth of substance (also referred to as rational truth) relates to the degree to which a calculation reflects all aspects of a defined concept. For instance, a depressive measure may lack legitimacy in substance because it only evaluates the defective aspect in distress but does not recognize the behavioral component.  

There is an aspect of rationality in deciding content validity that involves a level of consensus on what a specific characteristic of personalities like extroversion depicts. A conflict regarding a personality attribute would preclude the obtaining of legitimacy of a strong content.