The experience of brain injury changes the world for the person experiencing it and their family. It is important for health providers to know as accurately as possible how severe the brain damage is to be able to deliver the appropriate level of treatment and rehabilitation. Tests are available to measure current cognitive functioning which can be expressed as an intelligence quotient (IQ). One such test is the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV). Other tests are able to estimate premorbid IQ, for example the National Adult Reading Test (NART), the Test of Premorbid Functioning (TOPF) and the New Zealand Adult Reading Test (NZART). The discrepancy between the current IQ and the estimated premorbid IQ scores provides an estimate of the decrease in cognitive function as a result of brain injury. Most of these IQ tests have not been developed or normed for the New Zealand population and their suitability for this population is therefore not known. This study aimed to evaluate the ability of the tests of premorbid IQ to estimate the current WAIS-IV IQ in a New Zealand sample. This sample consisted of 86 New Zealand born, neurologically healthy, men and women (mean age of 46 years), who were administered the WAIS-IV, NART, TOPF and NZART. The results showed that the tests of premorbid IQ significantly over estimated lower IQ scores and significantly under estimated higher IQ scores. New regression formulae for the NART, TOPF and NZART were developed based on the WAIS-IV FSIQ and were found to be only marginally better at predicting current IQ. These new regression formulae also over-and under-estimated current IQ in the lower and upper ranges. The NZART, a New Zealand developed test, showed slightly better performance than the overseas tests. It was concluded that the tests of premorbid functioning are not very accurate in in their prediction of WAIS-IV current IQ for people in New Zealand and alternative methods of estimating premorbid IQ are suggested
