Elaboration, validation and standardization of the five to fifteen (FTF) questionnaire in a Danish population sample

• The largest study of the five to fifteen (FTF) questionnaire to date was carried out.
• We examined parent and teacher versions, the subdomain structure and impact questions.
• Scores had acceptable psychometric properties.
• Subdomains were organized into six domains.
• Impact questions yielded information above and beyond that provided by symptom count alone.

The five to fifteen (FTF) is a parent questionnaire developed to assess ADHD, its common comorbid conditions and associated problems in children and adolescents. The present study examined (1) the psychometric properties of scores on the new teacher version of the FTF, (2) competing models of the FTF subdomain structure and (3) the psychometric properties and utility of scores on the newly developed FTF impact questions. Parents (n = 4258) and teachers (n = 1298) of Danish children and adolescents (ages 5 to 17 years), selected using simple random sampling, completed the FTF. In the largest study of the FTF to date, parent and teacher scores had acceptable psychometric properties. The FTF subdomains were organized into six domains labelled cognitive skills, motor/perception, emotion/socialization/behaviour, attention, literacy skills and activity control and analysis of these domains may provide additional information when applying the FTF in the future. The impact questions yielded information above and beyond that provided by symptom count alone and appeared to increase the ability of the FTF to identify at risk children and adolescents.