Brief report: validity of Finnish registry-based diagnoses of autism with the ADI-R

Aims: The aim of the study was to explore the validity of registry-based diagnoses of autism in Finland using the Autism Diagnostic Interview - Revised (ADI-R). This study was designed for the Finnish Prenatal Study of Autism and Autism Spectrum Disorders (FIPS-A), an ongoing research project where registry-based diagnoses will be used for epidemiological studies. Methods: In this small pilot study, a clinical sample of 95 subjects diagnosed with childhood autism or pervasive developmental disorder/pervasive developmental disorder - not otherwise specified (PDD/PDD-NOS) or Asperger's syndrome according to the Finnish Hospital Discharge Register (FHDR) was gathered nationwide. A small control group consisting of siblings without any registered diagnoses of those being examined was also included in the study. Diagnoses were further re-evaluated by interviewing parents with the ADI-R. Results: The mean scores of autistic subjects clearly exceeded cut-off limits for autism on all three ADI-R domains and 96% of the subjects with registered diagnosis of childhood autism fulfilled the criteria based on the instrument as well. Conclusion: These results suggest that the validity of Finnish registry-based diagnoses of childhood autism can be considered good. Our findings lay important groundwork for further population- based studies of the aetiology of autism.