Variability of Trail Making Test, Symbol Digit Test and Line Trait Test in Normal People. A Normative Study Taking into Account Age-dependent Decline and Sociobiological Variables

Background And Aims: The influence of sociobiological variables and aging on the variability of the Trail Making Tests (TMT), the Symbol Digit Substituting Test (SDT), and the Line Trait Test (LTT) in the general healthy populations are not well known. Even less is known about the reliability at re-testing. This study aimed at determining the reference range of these tests, taking into account sociobiological variables and age, and the re-testing effect.

Methods: We studied 300 healthy subjects from 20 to 80 years of age. The sample was derived by the pooling of two samples stratified by age and sex: a randomized sample of 161 subjects collected from the city registers of Padova, and a convenience sample of 139 subjects collected in 20 towns (mainly rural) of Northern Italy. After normalization, data were assayed for the influence of age, education, job, and gender.

Results: Age was found to be a significant independent predictor for all the tests, education for all but the LTT, job only for the TMT-B and a geometrical version of the same test (TMT-G) which was proved to be highly correlated with the TMT-B (r=0.80, p<0.01). Job and the interaction age x education level influenced the difference TMT-B minus TMT-A. From the predicting equations, the normative data and the formulas to obtain Z scores for each test were derived. Reliability was lowest for LTT errors (CV=67%), highest for the SDT (13%), whereas the TMT obtained intermediate values (22-33%, depending on the test).

Conclusions: This study provides the most reliable normative data range for the TMT, SDT and LTT to date because it considers important demographic variables such as age, education and job.