In our view assessments begin with lots of validity - but, step by
step, it splashes away.
When examiners first think of a test or exam they imagine a perfect
test, with 100% validity.
At each step - as they specify the test, as they write questions and
mark schemes, as they select the ones
to put in the paper - a little
validity is lost.
More validity leaks out if the markers vary in how they award marks,
if the grade boundaries are not set so
as to maintain perfect standards, and
as teachers, selectors or employers
make decisions based on the results.
Throughout the process all the participants in assessment must do everything they can to maintain as much validity as possible.