Single case-control design for the study of the neuropsychological deficits and dissociations in Huntington’s disease-like 2

The Single-Case Methodology in Neuropsychology (Crawford & Howell, 1998) is a research design and robust inferential statistical method that facilitates the neuropsychological description of one case in terms of the differences between its profile and the performance of a carefully matched sample (Crawford & Garthwaite, 2012). The comparison is made by means of a t-test statistic that treats the normative sample as a sample and not as a population, with a particular effect-size associated with the size (n) of the sample. It is an ideal method for the neuropsychological investigation of rare diseases, such as Huntington’s Disease Like-2 (HDL2), especially when the cases are embedded in contexts of great diversity. This paper presents a step by step guide to the implementation of this method in a series of demographically and clinically diverse group of patients. • The application of a Single-Case Methodology in Neuropsychology enables the characterisation of rare diseases while controlling for demographic and context-related variables. • The implementation Single-Case Methodology in Neuropsychology provides test norms for homogenous groups that can be used by practitioners in their clinical work. • The method was customised for the South African population by controlling variables of specific relevance, such as linguistic diversity and quality of education.