Both the histogram picture and the test results refer to a nonnormal distribution for age (Kolmogorov-Smirnov: p < 0,05. Shapiro-Wilk: p < 0,01), WISC scores (Kolmogorov-Smirnov: p < 0,01. Shapiro-Wilk: p < 0,01) and BDI scores (Kolmogorov-Smirnov: p < 0,05. Shapiro-Wilk: p < 0,01). Boxplots revealed the existence of outliers for the WISC scores (case 21, score 41) and BDI scores (case 46, score 55). Although it is recommended in statistics to delete outliers, it was decided to maintain them in the present study due to their clinical value. Taking into consideration the above data about nonnormal distribution and the existence of outliers, nonparametric tests were applied.
During the exploratory analysis, it was examined whether the answers of the participants differed based on sex. For this purpose, the Mann-Whitney test was applied with sex as an independent variable and age, WISC scores and BDI scores as dependent variables [see Table 1, Additional File 1].
The results showed that for all three variables, there were no statistically significant differences between boys and girls in their answers (age U = 273,00, exact p = 0,67; WISC U = 183,50, exact p = 0,15; BDI U = 214,00, exact p = 0,23).
Research of diagnosis
In total, 50 children and adolescents with a mean age of 15 years participated in the study. A total of 42,9% of participants were boys, and 57,1% were girls. The application of the binomial test demonstrated that the distributions were not significantly different (exact p = 0,39). The mean WISC score of the participants was 95 points, and the mean BDI score was 17,7 [see Table 1, Additional File 1]. In Table 2 [Additional File 1], we present in detail the mean scores and standard deviations of each BDI question. The highest mean scores were observed for the questions “Change of sleep” and “Difficulty of concentration”, while the lowest mean scores were observed for the questions “Loss of interest in sex” and “Suicidal ideas”.
In regard to the total BDI score, we considered a score of 17 as the differentiating point of depressive mood, taking into consideration the proposal of Giannakou et al (2013) [32]. In the present research, 23 out of 47 BDI participants had a total score of 17 and above.
Distribution of diagnosis (diagnosis-related groups):
A total of 44,9% of participants were in the F30-F39 category [manic episode, bipolar affectional disorder, depressive episode, recurrent depressive disorder, persistent mood disorders (cyclothymia, dysthymia), other mood disorders (ICD-10)] [see distribution of diagnosis, Diagram 1, Additional File 2].
A total of 20,4% of participants were in the F40-F48 category [neurotic and somatoform disorders, such as phobic anxiety disorder, anxiety disorders, obsessive–compulsive disorder, adjustment disorders, dissociative disorders].
A total of 10,2% of participants were in the F50-F59 category [eating disorders, sleep disorders, sexual dysfunction, substance abuse. Importantly, this category includes anorexia nervosa].
A total of 2% of participants were in the F60-F69 and F70-F79 categories [personality disorders and mental retardation, respectively].
A total of 10,2% of participants were in the F80-F89 category [developmental disorders of speech and language, disorders of scholastic skills and pervasive developmental disorders].
A total of 4,1% of participants were in the F90-F99 category [hyperkinetic disorders, conduct disorders, emotional disorders with onset specific to childhood, tic disorders, disorders of social functioning with onset specific to childhood].
A total of 6,1% of participants were in the Double Diagnosis category.
Sleep disorders were also commonly reported on the BDI (22,4%).
Frequency distribution of BDI questions
The chi-square goodness-of-fit test was used to investigate whether the participants chose a score with the same frequency in each BDI question or whether they differed [see Table 3, Additional File 1] 1. As Table 2 [Additional File 1] portrays, the participants reported different answers except for on the questions regarding “Reduction of energy, Change of sleep, Difficulty of concentration”, where answers were distributed with more uniformity. In general, participants tended to select the first two scores, which refer to a lack of symptoms or less severe symptoms. The selection of higher scores, referring to more severe symptoms, was observed for the question regarding “Pessimism, Reduction of energy, Difficulty of concentration”.
In the last question referring to loss of interest in sex, the percentage of participants who did not answer the question reached 22,4%, and it is the highest compared to the rest of the questions (38 people versus 45 or 46). Thirty adolescents (61,2%) selected the answer “I have not noticed any recent change in my interest in sex”, 3 adolescents (6,1%) were less interested in sex than they used to be, 2 adolescents (4,1%) had almost no interest in sex, and 3 adolescents (6,1%) had lost interest in sex completely.
The vast majority of answers sums to the first score selection referring to answer “I have not noticed any recent change in my interest in sex”, which corresponds to a score of 0. Many of the participants had no history of sexual intercourse.
Among the BDI questions, only on question 12 (loss of interest) was there a statistically significant difference (early: 18,36, middle: 22,83, late: 31,32, χ2(2) = 6,99, p < 0,05).
In regard to sleep disorders in our sample, in the analytical form, the answers to BDI question 16 (Change of sleep) were distributed as follows:
I sleep as well as usual (0): 11 (22,4%)
I sleep a little more than usual (1a): 9 (18,4%)
I sleep a little less than usual (1b): 10 (20,4%)
I sleep much more than usual (2a): 5 (10,2%)
I sleep much less than usual (2b): 5 (10,2%)
I sleep most hours of the day (3a): 1 (2,0%)
I wake up 1-2 hours early and can’t go back to sleep (3b): 5 (10,2%)
Adolescence categories
For the investigation of a potential correlation between the adolescence period and the intelligence level and the BDI score, participants were divided into three categories: early adolescence (10-13 years), middle adolescence (14-17 years) and late adolescence (17-21 years). Fourteen of the participants belonged to the first category, 24 belonged to the second category, and 12 belonged to the third category. See distribution of diagnosis in boys and girls in Diagrams (Pie Charts) 2 and 3, respectively [Additional File 2].
Afterwards, the nonparametric Kruskal-Wallis test was applied with adolescence stage as the independent variable and WISC and BDI scores as the dependent variables.
WISC and BDI scores
The Kruskal-Wallis test showed that the median scores in each subcategory did not differ to a statistically significant degree in regard to the scoring of the participants in the WISC test (early: 20,68, middle: 21,89, late: 29,33, χ2(2) = 2,70, p = 0,26) and in the BDI (early: 23,92, middle: 23,46, late: 25,23, χ2(2) = 0,13, p = 0,94). Among the sub-questions of the BDI, a statistically significant difference was observed only in question 12 (loss of interest) (early: 18,36, middle: 22,83, late: 31,32, χ2(2) = 6,99, p < 0,05).
In conclusion, the participants did not differentiate as to their WISC and BDI scores in regard to the adolescence stage they were going through (early, middle, late). There is, however, the exception of the subquestion “Loss of interest”, where the highest scores were observed in late adolescence, while the lowest scores were observed in early adolescence.
Summary of results
The diagnosis distribution was as follows: 44,9% in the F30-F39 category, 20,4% in the F40-F48 category, 10,2% in the F50-F59 category, 2% in the F60-F69 and F70-F79 categories, 10,2% in the F80-F89 category, 4,1% in the F90-F99 category, and 6,1% in the double diagnosis category. No sex differences were observed. We found similar mean WISC scores (95 points) and BDI scores (17,7) between boys and girls. Higher BDI mean scores were noted for the questions “Changes in sleep” and “Difficulty in concentration”, while lower BDI mean scores were noted for the questions “Loss of interest in sex” and “Suicidal thoughts”. Twenty-three out of 47 BDI participants had a total score of 17 or more. In the questions assessing Pessimism, Reduction of energy and Difficulty in concentration, we observed higher scores that indicated more severe symptoms. In the question assessing a loss of interest in sex, the prevalence of missing answers was 22,4%, which is the highest in comparison to the other questions (38 people versus 45 or 46). The vast majority of participants selected the first score choice. No correlations were observed among age, WISC scores and BDI scores. WISC and BDI scores did not differ based on adolescence stage (early, middle, late). The only exception was the sub-question assessing loss of interest, where the highest scores were observed in late adolescence and the lowest scores were observed in early adolescence.