To the Editor: Dr Dales and colleagues1 reported that there was "essentially no correlation'' between rates of autism and measles-mumps-rubella (MMR) vaccine, but this conclusion is based on their Figure, which seems to be an optical illusion. We took the y-axis values directly from the Figure and computed the correlation coefficients, which are 0.73 and 0.90 between the total number of autism cases and the percentage of children receiving immunization by 24 months and 17 months, respectively. The illusion of no relationship is due to the vertically compressed graph. The apparent steepness of the autism curve may be attributed to the well-known epidemic effect of increased detection due to increasing vigilance.
Edwardes M, Baltzan M. MMR Immunization and Autism. JAMA. 2001;285(22):2852-2853. doi:10.1001/jama.285.22.2852