Peter Dunn and Margaret Marshman present the second of their data files articles in which they discuss the statistical investigation cycle which describes the whole process of conducting a statistical research study. [For "The Data Files: A Series of Articles to Support Mathematics Teachers to Teach Statistics," see EJ1259108.]

This article reports on gender ratio, age of diagnosis and the duration of assessment procedures in autism spectrum disorder diagnosis in a national study which included all types of clinical services for children and adults. Findings are reported from a retrospective case note analysis undertaken with a representative sample of 150 Scottish…