(a) In our sample, we had two questionnaires available that measured obsessive-compulsive symptoms: revised Obsessive-Compulsive Inventory (OCI-R, mean ± std: 7.33 ± 7.76, range: 0–50; Foa et al., 2002, Psychol Assess) and Padua Inventory Washington State University Revision (PI-WSUR, 17.09 ± 17.00, range: 0 - 106.5; Burns et al., 1996, Behav Res Ther). To build a general compulsivity composite score, we conducted an item-level principal component analysis (n = 1543 independent subjects in all panels) and used the first principal component thereof (PC1), in a similar approach as previous studies (Gillan et al., 2016, eLife; Rouault et al., 2018, Biol Psychiatry). Scree plot of PCA presented in (b) and the highest loading items of PC1 are shown in (c). This novel compulsivity component correlated highly with the total scores of both OCI-R (d) and PI-WSUR (e). Impulsivity differences and changes were assessed using BIS (Barratt Impulsiveness Scale total score, 64.19 ± 6.81, range: 39.7 - 114.5). We found that compulsivity and impulsivity were largely independent, sharing 1.4% of common variance (f). Pearson’s correlation coefficients were provided in panels a, d-f. In addition, both dimensions were only weakly associated with other psychiatric dimensions, such as anxiety (RCMAS total; Kiddle et al., 2017, Int J Epidemiol; impulsivity r = 10, compulsivity r = 35) or depression (MFQ total; Kiddle et al., 2017, Int J Epidemiol; impulsivity r = 06, compulsivity r = .33) thus showing relatively weak associations compared to other psychiatric dimensions (for example, correlation depression and anxiety r = .88) suggesting that our results are more specific to compulsivity and impulsivity than to a general psychopathology (Alnaes et al., 2018, JAMA Psychiatry). Notably, after correction for MFQ differences across individuals, effects presented in main results were still found (data not shown). Linear-mixed effects (LME) modelling (not shown, cf. methods and supplementary information) was applied to total scores of PI-WSUR and BIS, for which longitudinal follow-ups were available in the larger behavioural NSPN sample (for PI-WSUR (BIS): 533 (805) observations from 291 (305) subjects).