**6.2.3 Statistical analysis**

Prevalence rates of the Externalizing problem scale during the preschool years were calculated for mothers based on the norms provided by Achenbach and Rescorla (2000). Prevalence rates were calculated as a proportion of children with *subclinical* behaviour (T = 60 - 63) and *clinically relevant* behaviour (T ≥ 64). From the 2-year follow-up, the CBCL 4-18 with representative German norms was used. Percentages of ADHD and ODD mental health problems were calculated for all assessment points. Incidence rates are based on cumulative incidence for time periods as follows: pre-FU1, pre-FU2, pre-FU3, and pre-FU4.
