Definition
Validity
Validity is how well a measure, method, or conclusion addresses the question it is meant to answer.
What it means
First name the question. Then check whether the method really answers it. Counting how many library books a child owns would not validly measure how much they enjoy reading, because the count may reflect access rather than enjoyment.
Remember it
Right question, right method, right conclusion.
Example
A class wants to know how many minutes pupils read each day. Asking pupils to record their reading time for a week is more valid than asking how many books they own.
Watch for
Validity is always tied to a purpose or interpretation; a method can be useful for one question and unsuitable for another.
Common mix-up
Reliable results can repeat closely and still be invalid if the method measures the wrong thing.
Exact meaning
Validity concerns whether evidence and the way it was gathered support the intended interpretation or conclusion. A measure is valid for a purpose when it actually addresses the intended quantity or question, rather than a different one.