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.