Mean age of the children with ADHD was 11.5 yr. (SD 1.93), children with ID 11.6 yr. (SD 1.83) and for the TD children 11.5 yr. (SD 1.90). Most of the children were boys (n =32, 68%).
Missing data
There was no missing data in TPA. Regarding DTM, there was missing data from two children with ID. In self-rated autonomy, there was missing data from one child with ADHD and from nine children with ID.
Differences in TPA, DTM and autonomy between groups
Time-processing ability
There were statistically significant differences between the groups, F (2,138) = 84.49, p < .001. TD children had the highest scores for TPA, measured by KaTid and all data converted to KaTid-Youth, with a mean of 51.6 (SD 8.4), children with ADHD the second highest scores for TPA (mean 42.4, SD 11.0) and children with ID the lowest scores for TPA (mean 23.2, SD 12.6) (Table 1). There were statistically significant differences between children with ADHD and TD children (p < .001), children with ADHD and children with ID (p < .001) and children with ID and TD children (p < .001) with large ES on all comparisons (Table 1).
Daily time management
Statistically significant differences in daily time management were found between the groups, F (2, 138) = 27.45, p < .001. TD children had the highest scores for DTM (mean 66.2, SD 13.8) according to percent of maximum score of the Time-Parent scale (Table 1), children with ID had the second highest scores for DTM (mean 57.1, SD 17.1) and children with ADHD had the lowest scores for DTM (mean 44.6, SD 10.2). There were statistically significant differences between children with ADHD and TD children (p < .001), between children with ADHD and children with ID (p < .001 and between TD children and children with ID (p = .007). The ES were large or medium (Table 1).
Autonomy
There were statistically significant differences between the groups in autonomy, F (2, 130) 0 30.58, p < .00. TD children had the highest scores in both autonomy versions, followed by children with ADHD (Table 1). Children with ID had the lowest scores in both autonomy scale versions.
Using percent of maximum score based on both versions of autonomy TD children had the highest scores (mean 80.7, SD 10.4), children with ADHD the second highest scores (mean 76.0, SD 9.1) and children with ID had the lowest scores (61.3, SD 15.3). There were statistically significant differences between children with ADHD and children with ID (p < 0.001) and between TD children and children with ID (p < 0.001) with large ES.
Table 1 in about here.
Patterns of TPA in children with ADHD, children with ID and the TD children
The cluster analysis resulted in four clusters with different patterns of TPA, all based on the four subscales of TPA. The evaluation of the explained error sums of squares (69.70%) demonstrated an acceptable value. The homogeneity coefficient of the groups differed between 0.451 (Cluster C), 0.706 (Cluster B), 0.709 (Cluster A) and 1.131 (Cluster D), which is acceptable (Table 2).
Outliers
The first step in the cluster analysis was to identify a residue of outliers. The participants in the residue are held as being dissimilar to all other participants. There were two residuals found, both ID children. In total, 139 participants were included in the clusters.
Descriptives
There were statistically significant differences between clusters in age F (3.135) = 3.25, p = .024. The distribution of sex in the clusters varies between 57% and 86% boys. Still, there were no statistically significant differences in sex between the clusters (p = .756). There were statistically significant differences between clusters according to diagnosis (p < .001). Children with ADHD were represented in three of the four clusters and TD children in two. There were children with ID in all clusters. All clusters show the highest proportion of correct answers at the lower levels of TPA, i.e. time perception and time orientation/concepts, and a reduced ability at the higher levels, i.e. time orientation/objective time and time management (Figure 2). There were statistically significant differences in TPA between clusters F (3,135) =185.40, p < .001.
Figure 2 in about here.
Descriptions of the participants in each cluster according to number, sex, diagnosis, mean age, TPA (total score, time perception, time orientation (concepts and objective time) and time management). DTM and self-rated autonomy are presented in Table 2. The results for each cluster are presented separately below.
Table 2 in about here.
Cluster A - (Skilled in all levels of TPA)
Cluster A is the largest (n = 79) and contains children from all groups, but children with ID are underrepresented (11%). TD children make up the largest proportion (47%) followed by children with ADHD (42%). Mean age of the children is 11.8 (SD 1.92; range 8.72–15.73), i.e. the oldest children except for Cluster D (containing only children with ID). TD children in this cluster are the oldest of the TD children in the sample. Subgroup analysis of age in Cluster A showed that TD children had a mean age of 12.0 years, children with ADHD 11.7 years and children with ID 11.5 years.
According to TPA, these children have a mean of 82 % of total scores, which is the highest in the sample. Children in this cluster are skilled in all levels of TPA: time perception, time orientation (concepts and objective time) and time management (Figure 2).
Cluster B – (Skilled in time perception and time orientation/concepts)
Cluster B is the second largest (n = 46) and contains children from all groups, children with ID being overrepresented (52%). The distribution of TD children and children with ADHD is relatively even (26% and 22% respectively). Mean age of the children is 10.9 (SD 1.66; range 8.62–15.14), which means that it is the cluster with the youngest children. The TD children in this cluster are the youngest of the TD children in the sample. Subgroup analysis of age in Cluster B shows a mean age for TD children of 9.8, children with ADHD 11.2 and children with ID 11.2.
According to TPA, children in this cluster have a mean score which is the second highest, 58% of total scores. Children in this cluster are skilled in time perception and time orientation/concepts but have difficulties with time orientation/objective time and time management (Figure 2).
Cluster C – (Skilled only in time perception)
Cluster C is small (n=7), and contains children with ADHD and children with ID, children with ID being overrepresented (71%). Mean age is 11.1 (SD 1.42; range 9.44–13.50). Children with ID are older (M = 11.6) compared to children with ADHD (M = 9.7).
According to TPA, these children have a mean of 39% of total scoresi.e. the second lowest in the sample. Children in this cluster are skilled only in time perception and have difficulties with time orientation (both concepts and objective time) and time management (Figure 2).
Cluster D – (Difficulties at all levels of TPA)
Cluster D is small (n = 7), and contains only children with ID. Children in this cluster are the oldest in the sample with a mean age of 12.5 (SD 2.24; range 9.66–15.58).
According to TPA, these children have a mean of 24% of total scores, which is the lowest in the sample. The children have difficulties at all levels of TPA but mostly with time orientation/objective time and time management (Figure 2).
Diagnostic category and age related to pattern of TPA
Children with ADHD are represented in three clusters, i.e. not in cluster D (Difficulties at all levels of TPA). Most children with ADHD are found in Cluster A (Skilled in all levels of TPA), in which they are about as numerous as the TD children, and in Cluster B (Skilled in time perception and time orientation/concepts).
Children with ID are represented in all clusters, with the largest numbers found in Cluster B (Skilled in time perception and in time orientation/concepts), where they are overrepresented. They are also overrepresented in Cluster C, containing children skilled in time perception but having difficulties with all other levels of TPA and in Cluster D (Difficulties at all levels of TPA), containing children with the lowest scores of TPA.
The TD children are represented in two clusters, Cluster A (Skilled in all levels of TPA) (79% of TD children) and Cluster B (Skilled in time perception and time orientation/concepts).
Children in Cluster B (Skilled in time perception and time orientation/concepts) had the lowest mean age (10.9), followed by Cluster C (Skilled only in time perception) (11.1) and Cluster A (Skilled in all levels of TPA) (11.8). Children in Cluster D (Difficulties at all levels of TPA) had the highest mean age (12.5). The age range differs between clusters; Cluster A having the largest range (8.72–15.73) and Cluster C the smallest (9.44–13.50).
Daily time management and autonomy
DTM, as rated by the parents, is almost the same in all clusters, the exception being children in Cluster D (Difficulties at all levels of TPA), which has the lowest score (40% of maximum score). There were no statistically significant differences between the clusters.
There were significant differences in autonomy, as rated by the children themselves, between the clusters, F (3,125) = 15.98, p < .001. Children in Cluster A (Skilled in all levels of TPA) have the highest autonomy scores (78% of maximum score), followed by children in Cluster B (Skilled in time perception and time orientation/concepts) (71%), Cluster C (Skilled only in time perception) (60%) and the lowest scores in Cluster D (Difficulties at all levels of TPA), with 42% of maximum score. There were statistically significant differences between Cluster A and B (p = .003), Cluster A and C (p = .001), Cluster A and D (p < 0.001) and Cluster B and D (p < .001).