Which of the following is the best method of validity?
1. Content validity: Measurement of all variable components.
2. Consensual validity: If no. of experts agree to a parameter.
3. Criterion validity: If compared with a reference or gold standard.

It is the best measure of validity.
Usually expressed as sensitivity & specificity. 

4. Discriminant validity: If not showing a strong correlation between 2 variables.
Content validity
Criterion validity
Consensual validity
Discriminant validity