Validity

Validity is the extent to which a study measures what it claims to measure and supports the conclusions drawn from it. Where reliability concerns consistency, validity concerns accuracy — and the two are independent, since a measure can be perfectly consistent and still measure the wrong construct.

Measurement validity has several strands: face validity (does it look right), content validity (does it cover the full concept, usually judged by expert review), criterion validity (does it correlate with an established measure or predict a relevant outcome), and construct validity (convergent and discriminant evidence).

Design validity has two further strands. Internal validity concerns whether the study genuinely rules out alternative explanations for the observed effect, and external validity concerns whether the findings transfer to other populations, settings and times. Address each explicitly in your methodology and limitations sections.