In the medical and social research concerning "sexual activity" of man or woman, for example:
Nevertheless, clefts were found in both the sexually active and the never-active groups: 20 of their 200 never-sexually-active subjects possessed complete hymenal clefts, as did only 84 of their 100 sexually active subjects
Is the status "sexually-active" usually self-reported by the patients? How trustworthy is this data? What if someone misreport their status? What are some mechanisms to prevent lies?