Developmental, Dimensional and Diagnostic Interview

The Developmental, Dimensional and Diagnostic Interview (3di) is a standardized interview unique in its construction. It is neither fully structured nor semi-structured, but a hybrid between the two systems, using the strengths of both approaches. Highly structured interviews can achieve excellent reliability, but validity and patient acceptability suffer. Semi-structured interviews, which rely strongly on interviewer judgment for scoring, can achieve good discriminant validity and acceptability, but achieving good reliability requires intensive initial training, and ‘rater drift’ can occur over time without regular retraining. The 3di is a computerized interview, currently configured to run on any Microsoft Windows format. Computerization of the interview procedure has made it possible to cluster questions according to main domains of function or adjustment, such as medical history, language, non-verbal communication, play and friendships, as well as subdomains, such as sharing possessions, spontaneous affection and imaginative social play. We have avoided structures that are strictly diagnostic in format. As parents become increasingly sophisticated informants about symptomatology associated with particular diagnoses, especially autistic disorders or ADHD, there is a risk of respondent bias. Breaking down complex questions and scattering their components throughout the interview is an effective way of dealing with this problem.