Information by Design
Lifestyle Survey Toolkit

Validity is the degree to which an item measures what it is intended to measure.  Important aspects here are:

• Context and face validity - does the item include all relevant aspects; does it look reasonable?
• Criterion validity - how does the item compare to any 'gold standard'
• Construct validity - how does the item correlate with other measures in the questionnaire

To measure context face validity it is normal to form an 'expert panel' who assess the items in the questionnaire.  Construct validity is measured using by examining how the scale under development correlates with other instruments (scales).