Reliability of parent recall of symptom onset and timing in autism spectrum disorder

Past events are often reported as occurring more recently than they actually took place, an error called forward telescoping. This study examined whether forward telescoping was evident in parent reports of autism spectrum disorder symptom emergence and onset classification. Parents were interviewed when their child was 2–3 years old (Time 1) and approximately 6 years old (Time 2). Significant forward telescoping was found in both age of social regression and age when language milestones were achieved, but not age of language regression. The correspondence between Time 1 and Time 2 onset report was low (kappa = 0.38). Approximately one-quarter of the sample changed onset categories, most often due to parents not recalling a regression at Time 2 that they had reported at Time 1. These results challenge the use of retrospective methods in determining onset patterns.