sentences:  There is no incentive for patients to report their outcome data other than to "pay it forward" to the community and help the health industry prevent unnecessary suffering in other patients.A well-designed PRO questionnaire should assess either a single underlying characteristic or, where it addresses multiple characteristics, should be a number of scales that each address a single characteristic.These measurement "characteristics" are termed "constructs" and the questionnaires used to collect them, termed "instruments", "measures", "scales" or "tools".