Designing Effective Assessment
There are different types of validity, including content validity. Content validity refers to the extent a test measures what it claims to measure. There must be a genuine relationship between the task and the learning required to complete the task. A valid assessment task will be a measure student's learning (and not something else).
The ability to complete an assessment task successfully should, thus, be dependent on the student learning what is required in the course or unit of study. If the student is able to do the task without that learning, the assessment is not a valid measure of student learning. An essay task may measure of students' essay writing skills rather than their ability to apply discipline knowledge.
Hence, a valid assessment does not require knowledge or skills that are irrelevant to what is actually being assessed. Examples include: ability to read, write, role-play, or understand the context; personality; physical limitations; or knowledge of irrelevant background information.
In order to provide sound evidence of the extent of a student's learning; the assessment must be representative of the area of learning being assessed. Assessing content randomly selected from 6 weeks only of a 13 week semester, for an end of semester exam, is not representative; and will not validly measure a student's overall learning achievement. A student with solid overall knowledge of the entire semester's work can still fail such a narrow exam as adequate opportunity to demonstrate their learning is not possible.
Validity can also relate to the value of an assessment task in preparing students for what they will be required to do once they have graduated. Students need to see clear links to how the assessment is related to their future roles.
Valid assessment will be a measure of student learning (not something else); and the extent of that learning.