I'm with a group of physical therapy students planning a research study. We are looking at back pain in older adults and measuring it against their function. Can we rely on patients to answer our questions honestly to get an accurate result?

If we didn't there's a lot of research that would never get done or reported. Assessing skills based on self-report is both reliable and valid.

You can find out more about this with a study published back in 1987 [Jette AM: The Functional Status Index: Reliability and Validity of a Self-Report Functional Disability Measure. Journal of Rheumatology. 14 (Supplement 15). Pp. 15-19].