An investigation of the use of standardised leaving certificate performance as a method of estimating pre-morbid intelligence

In cases of brain pathology, current levels of cognition can only be interpreted reliably relative to accurate estimations of pre-morbid functioning. Estimating levels of pre-morbid intelligence is, therefore, a crucial part of neuropsychological evaluation. However, current methods of estimation have proven problematic.

To evaluate if standardised leaving certificate (LC) performance can predict intellectual functioning in a healthy cohort. The LC is the senior school examination in the Republic of Ireland, taken by almost 50 000 students annually, with total performance distilled into Central Applications Office points.

A convenience sample of university students was recruited (n = 51), to provide their LC results and basic demographic information. Participants completed two cognitive tasks assessing current functioning (Vocabulary and Matrix Reasoning (MR) subtests - Wechsler Abbreviated Scale of Intelligence, Second Edition) and a test of pre-morbid intelligence (Spot-the-Word test from the Speed and Capacity of Language Processing). Separately, LC results were standardised relative to the population of test-takers, using a computer application designed specifically for this project.

Hierarchical regression analysis revealed that standardised LC performance [F(2,48) = 3.90, p = 0.03] and Spot-the-Word [F(2,47) = 5.88, p = 0.005] significantly predicted current intellect. Crawford & Allen's demographic-based regression formula did not. Furthermore, after controlling for gender, English [F(1,49) = 11.27, p = 0.002] and Irish [F(1,46) = 4.06, p = 0.049) results significantly predicted Vocabulary performance, while Mathematics results significantly predicted MR [F(1,49) = 8.80, p = 0.005].

These results suggest that standardised LC performance may represent a useful resource for clinicians when estimating pre-morbid intelligence.