Use of psychometric measures and nonorganic signs testing in detecting nomogenic disorders in low back pain patients

The effect of financial compensation on responses to psychometric testing was studied in 231 chronic back pain patients. Item by item comparison of responses to two tests, readministered within 4 hours, yielded inconsistency scores. These inconsistency scores, along with scores on other psychometric measures and on Waddell's nonorganic signs test, of a group of 97 patients anticipating or receiving financial compensation (AFC), and a group of 134 patients not receiving or anticipating financial compensation (non-AFC) were compared. The AFC group had significantly higher mean scores than did the non-AFC group on the inconsistency measures, on almost all psychometric tests and on nonorganic signs. Almost all non-AFC subjects scored "0" on nonorganics, whereas 83% of AFC subjects scored "2" or higher. Prediction analysis revealed that the nonorganics score alone can predict AFC/non-AFC status; 90% of subjects were correctly classified. The inconsistency scores correctly classified 78%. Together, they correctly classified 93%. It was concluded that nonorganic scores and inconsistency scores (as defined by the investigators) distinguish between, and can predict membership in AFC and non-AFC groups. The significantly higher inconsistency scores obtained by the AFC group suggest that these psychometric test results are unreliable and hence invalid for this group.