This figure has been published in a book chapter on the epidemiology of autism spectrum disorders (ASD), in which we discuss methodological factors impacting the estimation of prevalence and the interpretation of changes in prevalence estimates over time. All co-authors did not love this figure in particular, but at the time, we could not figure out a better way to illustrate the concept.
The main point of the figure (using simplistic hypothetical numbers) is to highlight a methodological confound in studies that use what are called “referral statistics”, that is, they estimate prevalence of ASD based on the number of individuals with ASD referred for specialist services or special education registers. Studies that rely solely on referral statistics to estimate prevalence of ASD can show large increases in prevalence of ASD between two time points, but this increase may not be due to an actual increase in the number of individuals affected by ASD. Patterns in referral statistics for ASD are necessarily confounded by referral patterns, availability of services, heightened public awareness, decreasing age at diagnosis, and changes over time in diagnostic concepts and practices.
I don’t have any immediate plans for using this figure again, but would love some ideas for illustrating this point visually. Solutions in R would be most helpful, but any ideas are welcome.
May 6, 2015