Estimation of premorbid cognitive function based on word knowledge: the Swedish Lexical Decision Test (SLDT)

In clinical neuropsychology, the present status of a patient is evaluated in relation to the assumed premorbid status. However, in Sweden, existing methods to assess premorbid status are far from optimal. In the present study, the design and evaluation of a Swedish Lexical Decision Test (SLDT) for premorbid global cognitive function (i.e., premorbid intelligence) is described. The design was based on the empirical finding that, in general adult population, word knowledge is strongly associated with measures of global cognitive functioning. Linear stepwise regression analysis demonstrated that SLDT findings accounted for 48% of the variance of global cognitive function as assessed by the Full Scale Intelligence Quotient (FSIQ) from the Wechsler Adult Intelligence Scale Revised (WAIS-R). Demographic variables alone accounted for 31% and a combination of SLDT results and demographics accounted for 60%. Psychometric properties are presented using data from 109 healthy individuals stratified according to age, gender, and level of education. In addition, a case of Alzheimer's disease is presented to illustrate the relationship between SLDT performance and cognitive function. Finally, the theoretical foundation for the relationship between word knowledge and global cognitive function is discussed.