mainly for research purposes. The ADI was developed in response to four major developments in the field of diagnosing autism which led to a need for updated diagnostic tools. These developments included improvements in the diagnostic criteria, the need to differentiate between autism and other developmental disorders that appear similar early in life, and the desire, in the area of psychology, for standardized diagnostic instruments. The original ADI could be used on individuals with a chronological age of at least five years and a mental age of at least two years, but autism spectrum disorder is usually diagnosed much earlier than this age. This finding led Rutter, LeCouteur, and Lord to revise the ADI in 1994 so that it could be used to determine a diagnosis in individuals with a mental age of at least 18 months. This would enable clinicians to use the interview to differentiate autism from other disorders which can appear in early childhood. The writers' main goals in revising the ADI were to make the interview more efficient, shorter, and more appropriate for younger children. The majority of the revisions made involved the organization of the interview. The questions were divided into five distinct sections and early and current behavior were consolidated in each section. Research led to some modifications of specific interview questions. Modifications included both making some questions focus more on autism-specific aspects of behaviors and making other questions more generalized to improve efficiency. Also, some additional questions were added to the interview, including more specific questions about ages when abnormal behaviors began. Other irrelevant items were removed in order to increase the interview's ability to diagnose autism at a younger age. These question revisions also led the writers to revise the scoring algorithm and cut-off scores as there were more questions added to some sections. Reliability Questions from the original version of the ADI that were found, through research, to be unreliable or not applicable were removed when the interview was revised. The ADI-R has also been tested thoroughly for reliability and validity using inter-rater reliability, test-retest reliability and internal validity tests. The results of this research have led to the ADI's acceptance among both researchers and clinicians for decades. The ADI-R is often used in conjunction with other related instruments to determine an autism diagnosis. The writers have published psychometric results that indicate both reliability and validity of the ADI-R. Both inter-rater