Validity is often confused with reliability but it is important to distinguish between the two concepts. Validity relates to how well a device or procedure measures what it is intended to measure. The source of the confusion is that one cannot have validity if there is little reliability and over repeated measurements where one keeps getting different answers. I will return to the issue of reliability in later blogs, but for now let’s focus on validity and how to test it for the new pain scoring component of SortED tablet (OUCH™).