The increase in the incidence of autism from 1990 on may be attributable to more attention being drawn to the syndrome of autism and to achange in the diagnostic criteria from the ICD-8 to the ICD-10 in 1994. Also, outpatient activities were included in the Danish Psychiatric Central Research Register in 1995 and because many patients with autism in former years have been treated as outpatients this may exaggerate the incidence rates, simply because a number of patients attending the child psychiatric treatment system before 1995 were recorded for the first time, and thereby counted as new cases in the incidence rates.
Madsen et al., Thimerosal and the Occurrence of Autism: Negative Ecological Evidence From Danish Population-Based Data, Pediatrics 2003;112;604-606
The Madsen study above is one of the studies referred to by those who assert that "science" has proven that thimerosal in vaccines does not cause or contribute to autism. The usual reference to this study is that after thimerosal was removed from Danish vaccines in 1992 incidence of autism continued to rise. As the authors themselves pointed out the continued rise in autism in Denmark after the removal of thimerosal coincided with changing diagnostic criteria, increased social awareness and different methods of outpatient recording. It is truly amazing that those who assert that vaccines do not cause autism based on such studies now claim that data showing autism diagnoses increases from 1 in 150 to 1 in 91 during the latter half of this decade, more than a decade after the DSM and ICD diagnostic changes. does not necessarily reflect a true rise in autism for the reasons set out in the Madsen quote above.
Should we not also discount the Madsen study, and the claims that thimerosal has been proven safe, because of diagnostic and social awareness changes? Or should we accept the recent data showing increased diagnoses of autism as reflecting a real increase in autism diagnoses>
Which is it Dr. Insel? And what do you think Dr. Offit?