Reliability of a test as a questionnaire means that the questionnaire is measuring something in a reproducible way. Validity on the other hand means that the questionnaire is measuring what is intended to. In situations where other scales of the same or similar attributes are available, outcomes of an existing scale and the new one administered to a sample of people may be compared with their correlation indicating the validity of the new scale. However, if no other measure pre-exists, another approach is necessary called ´construct validity´.(1) read more