Discrepancy analysis and Australian norms for the Trail Making Test

Discrepancy analyses refer to comparison methods that evaluate the relationship or differences between two measures in the same individual. A common type of discrepancy analysis involves the comparison of two trials within a measure, such as, Trails A and B of the Trail Making Test (TMT). The TMT is well-suited to this role as the two measures are highly correlated, assess similar underlying constructs, and most importantly demonstrate differential vulnerability to the impact of pathology. While the inclusion of these types of data in the form of difference scores or ratios has become more frequent, this information has been presented only for demographically adjusted subgroups and has not taken into account the level of performance of the comparison trial, Trails A.

The role and advantages of discrepancy analysis with the TMT stratified by level of Trails A performance were demonstrated with an Australian normative sample of 647 participants and a heterogeneous clinical sample consisting of 2,292 Australian and U.S.

The ability to differentiate between the influence of slowed visual scanning and/or graphomotor speed, and reduced mental flexibility was demonstrated by applying the normative data to clinical case discrepancies. The importance of accounting for the variability in discrepancy scores associated with the level of performance of Trails A was also highlighted.

A simple, efficient, and effective approach to examining the basis for differences between TMT-A and TMT-B performances is provided to examine the relative contributions of perceptual/motor abilities, and mental flexibility.