The estimation of premorbid functioning has become increasingly important in neuropsychological assessment (O’Carroll, 1995) due to issues such as litigation following brain injury and accuracy of dementia diagnosis (Reynolds, 1997). Premorbid estimations provide a baseline for clinicians to establish any decline in cognitive functioning (Berg, Durant, Banks, & Miller, 2016; McDonald, 2015). It is important to compare an individual’s current performance to their own individualised comparison standard as what may be considered as a normal level of functioning for one individual, may be considered an impairment in another (Crawford, 1992; Crawford, Miller, & Milne, 2001; Lezak, 2004). However prior functioning data is not always available.
