Participant characteristics are presented in Table 1 (children and adolescents) and Table 2 (parents).
Table 1
Descriptive characteristics of the children and adolescents included in Model 1 and Model 2. Children in Model 3 and Model 4 are a subsample of the children.
| Children and adolescents with OCD | Children and adolescents without OCD | Test (p-value) |
n | 113 | 88 | |
Age (years) | | | 0.26A |
| Mean (SD) | 13.37 (2.83) | 12.92 (2.78) | |
| Median (min, max) | 13.81 (8.08, 17.99) | 12.37 (8.09,17.83) | |
| Missing (n) | 0 | 0 | |
Sex (n (%)) | | | 0.98B |
| Female | 58 (51.3%) | 45 (51.1%) | |
| Male | 55 (48.7%) | 43 (48.9%) | |
| Missing | 0 | 0 | |
Pubertal stage (n (%)) | | | 0.39B |
| Pubertal stage 1 | 32 (28.3%) | 23 (26.1%) | |
| Pubertal stage 2 | 13 (11.5%) | 20 (22.7%) | |
| Pubertal stage 3 | 20 (17.7%) | 14 (15.9%) | |
| Pubertal stage 4 | 25 (22.1%) | 23 (26.1%) | |
| Pubertal stage 5 | 13 (11.5%) | 8 (9.1%) | |
| Missing | 10 (8.8%) | 0 (0%) | |
Nationality (n (%)) | | | - |
| Danish | 95 (84,1%) | 63 (71.6%) | |
| Other | 3 (2.7%) | 2 (2.3%) | |
| Missing | 15 (13.3%) | 23 (26.1%) | |
Comorbid psychiatric disorders (n (%)) | | - | - |
| Anxiety disorders ICD-10 F40-41, F93 | 12 (10.6%) | - | |
| Stress and adjustment ICD-10 F43 | 12 (10.6%) | - | |
| Asperger’s Syndrome ICD-10 F84.5 | 14 (12.4%) | - | |
| Hyperkinetic disorders ICD-10 F90.0 | 13 (11.5%) | - | |
| Tic disorders ICD-10 F95 | 13 (11.5%) | - | |
| Other* | 20 (17.7%) | - | |
Medication (n (%)) | | - | - |
| Children receiving medication* | 24 (21.2%) | - | |
Somatic disorders (n (%)) | | - | - |
| Children with a somatic disorder* | 32 (28.3%) | - | |
* Other describes all other diagnoses. For detailed information on patient medication and comorbid and somatic disorders see Appendix 4. At-test, BChi-squared test. Note: n, number; SD, standard deviation; OCD, obsessive-compulsive disorder; ICD-10, International Classification of Diseases-10
Table 2
Descriptive characteristics of parents included in Model 4
| Children and adolescents with OCD | Children and adolescents without OCD |
n | | |
| Mothers | 92 | 58 |
| Fathers | 72 | 32 |
Mother age (years) | | |
| Mean (SD) | 45.72 (5.03) | 45.97 (5.10) |
| Median (min, max) | 45.61 (32.76,56.24) | 46.45 (34.97,57.19) |
| Missing (n) | 0 | 0 |
Father age (years) | | |
| Mean (SD) | 48.17 (5.67) | 47.47 (6.78) |
| Median (min, max) | 48.91 (33.1,73.51) | 47.08 (34.45,62.73) |
| Missing (n) | 0 | 0 |
Nationality Mother (n (%)) | | |
| Danish | 77 (83.7%) | 46 (79.3%) |
| Other | 5 (5.4%) | 3 (5.2%) |
| Missing | 10 (10.9%) | 9 (15.5%) |
Nationality Father (n (%)) | | |
| Danish | 57 (79.2%) | 24 (75%) |
| Other | 5 (6.9%) | 1 (3.1%) |
| Missing (n) | 10 (13.9%) | 7 (21.9%) |
Parental education mothers (n (%)) | | |
| Upper secondary education or below | 8 (8.70%) | 1 (1.7%) |
| Short-cycle tertiary education | 14 (15.2%) | 3 (3.2%) |
| Bachelor’s degree or equivalent | 38 (41.3%) | 22 (37.9%) |
| Master’s degree or above | 22 (23.9%) | 23 (39.7%) |
| Missing (n) | 10 (10.9%) | 9 (15.5%) |
Parental education fathers (n (%)) | | |
| Upper secondary education or below | 12 (16.7%) | 3 (9.4%) |
| Short-cycle tertiary education | 8 (11.1%) | 3 (9.4%) |
| Bachelor’s degree or equivalent | 16 (22.2%) | 6 (18.8%) |
| Master’s degree or above | 25 (34.7%) | 13 (40.6%) |
| Missing (n) | 11 (15.3%) | 7 (21.9%) |
Note: n, number; SD, standard deviation; OCD, obsessive-compulsive disorder |
In Model 1, salivary oxytocin concentrations did not significantly differ between children and adolescents with and without OCD (p = 0.2682, Table 3 and further details in Appendix E), but the Bayes factor showed only anecdotal support for the H0 hypothesis (BF10 = 0.37, Table 3), a result which was particularly sensitive to the prior distribution (see Appendix C).
Table 3
Result of student’s t-test of salivary oxytocin levels in children and adolescents with and without OCD (OCD-status) and Bayesian statistics (Model 1)
| | | t-statistics | p-value | Bayesian analysis |
Model 1 | | | | | |
1. Test | H1 | OCD-status | 1.111 | 0.2682 | BF10 = 0.37 |
H0 | Intercept | | | |
Note. BF, Bayes factor; H1, alternative hypothesis; H0, null hypothesis |
In Model 2, the age-sex interaction, sex, and OCD-status did not significantly contribute to variation in child and adolescent oxytocin and were thus removed in the first three steps (see Appendix E). The reduced model showed a significant positive linear relationship [Figure 2 and Fig. 4 (pink line)] between age and child and adolescent oxytocin (p = 0.0031, Table 4, and see Appendix E). The Bayesian analysis showed that the model including child and adolescent age had a better predictive performance but a large standard error (SE) (ELPD-LOO = -3.4, SE = 2.7, Table 4). When we reexamined the relationship between child and adolescent oxytocin and OCD-status while controlling for age, OCD-status did not significantly account for variation in oxytocin (p = 0.3605, Table 4, and see Appendix E). The corresponding Bayes factor showed moderate support for no difference in oxytocin concentrations between children and adolescents with and without OCD controlling for age (BF10 = 0.31, Table 3) but with considerable prior sensitivity (see Appendix C).
Table 4
Results of reduced models, reduced models with OCD, and Bayesian statistics of Model 2 and Model 3
| | | F-statistics | p-value | Bayesian analysis |
Model 2 | | | | | |
1. Test | H1 | Reduced model (age) | 8.913 | 0.0031 | H1- H0 ELPD-LOO (SE) = 3.5(2.7) |
H0 | Intercept | | | |
2. Test | H1 | Reduced model (age) and OCD-status | 0.840 | 0.3605 | BF10=0.31 |
H0 | Reduced model (age) | | | |
Model 3 | | | | | |
1. Test | H1 | Reduced model (pubertal stage) | 5.384 | 0.0004 | H1- H0 ELPD-LOO (SE) = 6.6(4.1) |
H0 | Intercept | | | |
2. Test | H1 | Reduced model (pubertal stage) and OCD-status | 2.113 | 0.1477 | BF10=0.52 |
H0 | Reduced model (pubertal stage) | | | |
Note: BF, Bayes factor; H1, alternative hypothesis; H0, null hypothesis; ELPD-LOO, expected log-pointwise predictive density estimated by leave-one-out cross validation; SE, standard error |
In Model 3, the pubertal stage-sex interaction, sex, and OCD-status were removed in the first three steps as they did not significantly contribute to the variation in child and adolescent oxytocin (see Appendix E). The reduced model showed a significant relationship (Fig. 3) between child and adolescent oxytocin and pubertal stage (p = 0.0004, Table 4 and see Appendix E). Bayesian analysis showed a better predictive performance of a model including pubertal stage, but with a large standard error (ELPD-LOO=-6.5, SE 4.1, Table 4). When controlling for pubertal stage, OCD-status did still not significantly account for variation in oxytocin (p = 0.1477, Table 4 and Appendix E). The corresponding Bayes factor showed anecdotal support for no difference in oxytocin concentrations between children and adolescents with and without OCD controlling for pubertal stage (BF10 = 0.52, Table 4) with considerable prior sensitivity (see Appendix C).
In Model 4, including children and adolescents, and parents, the age-sex interaction and sex did not significantly contribute to the variation in oxytocin and were removed from the model in the first two steps (see Appendix E). The reduced model showed a significant positive, linear relationship [Figure 4 (blue line)] between participant age and oxytocin (p < 0.0003, see Appendix E).
The reduced exploratory Post Hoc Model A showed a significant relationship between oxytocin and quadratic age [Figure 2 and Fig. 4 (purple line); p = 0.0496, see Appendix E].
Post Hoc test B showed that the predictive performance of the model including pubertal stage and OCD (reduced Model 3 with OCD) was slightly better than the model with quadratic age and OCD (reduced Post Hoc Model A and OCD) (ELPD-LOO = 2.9, SE 3.0, see Appendix C). However, the standard error of the difference in predictive performance was large.
Visual inspection of Fig. 4, illustrating the reduced Model 2 (child and adolescent age, pink line), the reduced Post Hoc Model A (child and adolescent quadratic age, purple line), and the reduced Model 4 (child, adolescent, and parent age, blue line), indicates that the models in children and adolescents cannot be extrapolated to adults and the model in all participants seemed problematic in estimating in children and adolescents.
In Post Hoc Model C, we used “pubertal stage 6” for the adults and found a significant relationship (Figure E.1 in Appendix E) between salivary oxytocin and the modified pubertal stage in the sample including children, adolescents, and adults (p = 0.005, see Appendix E). The Bayesian analysis showed a better predictive performance of the model with the modified pubertal stage compared to the model with age (ELPD-LOO = 5.9, SE 5.1, see Appendix C).
In Post Hoc Model D, including only adults, the age-sex interaction, sex, and age did not contribute to the variation in oxytocin (p = 0.10, see Appendix E).
Sensitivity analyses of the Bayesian analyses of the models showed a general sensitivity to priors and little difference in predictive performance between the compared models with high standard errors (Appendix C).
The random forest analysis in children and adolescents alone and in children, adolescents, and adults indicated that pubertal stage/modified pubertal stage and age were the most important variables. Furthermore, these findings both in visual presentation of the predictions and the mean squared error (MSE) resembled the findings from the linear models (see Appendix D).
In the additional analyses in our appendix, we found that adult females had significantly higher oxytocin concentrations during menstruation than during ovulation (see Appendix F). The remaining analyses were not statistically significant.