Reasons why self-reported information may be misleading:
(1) consequence of reporting - risk (leads to underreporting) or benefit (leads to over-reporting)
(2) desire to please observer
(3) bias in observer
(4) fear or distrust of the observer
(5) discrepancy between self-image and reality (for example reported vs real weight)
(6) awareness of problem - denial (leads to underreporting) or neurosis (leads to over-reporting)
(7) poor memory or recollection of facts
(8) likelihood that the information can or will be checked
(9) personal attitude towards truthfulness and lying
(10) intention to mislead or manipulate
Methods of validating information:
(1) direct measurement (height, weight, etc.) or observation
(2) measurement of surrogate marker
(3) corroboration by family member or witness
