The Trail Making Test (TMT; Army Individual Test Battery, 1944) is among the most commonly-used neuropsychological tests in clinical practice (Rabin, Barr, & Burton, 2005), in part because it is among the instruments most sensitive to brain damage (Reitan & Wolfson, 1994). The cognitive alternation required by Part B reflects executive functioning, although other cognitive abilities, such as psychomotor speed and visual scanning, are also required for the successful completion of the test (Lezak, Howieson, & Loring, 2004). Despite early research suggesting that TMT performance is independent of age (Boll & Reitan, 1973), newer recent studies using larger and more representative samples have reported declining performance with increasing age (e.g., Ivnik, Malec, Smith, Tangalos, & Petersen, 1996; Kennedy, 1981; Rasmusson et al., 1998).
TMT normative data have been reported in many studies using a wide variety of sample demographics (e.g., Tombaugh, 2004). Larger-scale efforts examining performance include the Mayo Older Adults Normative Study (Ivnik et al., 1996) and the Revised Comprehensive Norms for an Expanded Halstead-Reitan Battery (Heaton, Miller, Taylor, & Grant, 2004). Most published normative data for the TMT capture time to completion. Additional research has examined the clinical value of a ratio (B/A; Giovagnoli et al., 1996) or difference score (B-A; Arbuthnott & Frank, 2000) between the two TMT conditions. The ratio score in particular has been examined as a symptom validity indicator (O’Bryant, Hilsabeck, Fisher, & McCaffrey, 2003; Ruffolo, Guilmette, & Willis, 2000). Frequency of errors, while often recorded and reported clinically, has not been empirically evaluated in prior TMT normative studies. Some investigators have pointed out that the examiner’s correction of errors adds additional time to the total score, thus accounting for difficulties reflected in the number of errors (Stuss et al., 2001).
The TMT error rate is difficult to interpret in isolation, particularly because errors are common among cognitively normal adults. In one study, 34.7% of control participants committed at least one error on TMT Part B (Ruffolo et al., 2000). Stuss and colleagues (2001) examined error rates in brain-lesioned patients and lesion location (i.e., frontal vs. nonfrontal). For a cutoff of >1 error, they found high positive predictive power (i.e., high error rate suggests presence of frontal lesion vs. other lesion) but poor negative predictive power (i.e., less than 2 errors does not necessarily implicate a nonfrontal lesion). Some have found that head-injured individuals are more likely to commit errors and less likely to correct them without prompting (e.g., Armitage, 1946), though other studies failed to distinguish head-injured participants from controls based on errors (Klusman, Cripe, & Dodrill, 1989).
Three different TMT error types have been identified (Mahurin et al., 2006; McCaffrey, Krahula, & Heimberg, 1989), including: (1) sequential or tracking errors (proceeding to the incorrect number or letter on Part A or B); (2) perseverative errors (failure to proceed from a number to a letter, or vice versa, on Part B); and (3) proximity errors (proceeding to an incorrect nearby circle on Part A or B). Mahurin and colleagues (2006) examined TMT errors, time to completion, and other neuropsychological measures among patients with schizophrenia and depression as well as healthy controls. While healthy controls completed both parts faster than the patients with depression (who completed each part faster than the patients with schizophrenia), elevated error rates were only observed in the schizophrenia group. Regression analyses implicated visual search in TMT A time performance, processing speed and mental tracking in TMT B time score, and mental tracking ability in TMT B error rate. However, a nonstandard administration was used in this study, as errors were not corrected by the examiner.
The purpose of the present investigation was twofold: (1) to provide normative data for TMT total errors in cognitively normal older participants, and (2) to determine the diagnostic accuracy of TMT B errors in a sample consisting of cognitively normal elderly and individuals meeting diagnostic criteria for mild cognitive impairment (MCI) or Alzheimer’s disease (AD).