Assessing olfactory abilities with the University of Pennsylvania smell identification test: a Rasch scaling approach

The strategy of delaying or retarding the progression of Alzheimer's disease requires early diagnosis and treatment. Previous research indicates that measurement of changes in olfaction and cognition will play an important role in the early detection of AD and in the monitoring of therapy effectiveness. Using the data of 177 subjects, our objective was to study the measurement properties of the University of Pennsylvania Smell Identification Test (UPSIT) using a Rasch scaling framework. The results indicate that the UPSIT can yield a linear, unbiased, and unidimensional Rasch measure of human smell recognition abilities. As expected, olfactory recognition ability decreased with age, and at the rate of about 0.05 Logits per year. Also, Alzheimer's patients showed a decrease in smell recognition equivalent to that experienced by healthy subjects over the course of 30 years. Hormone replacement therapy was not found to affect healthy women's olfactory recognition ability. Additional diagnostic information can be extracted from the analysis of incorrect responses patterns that is relevant to group membership.