The aim of this post-hoc analysis was to evaluate and validate the newly devised GIPD scale that measures the degree of ADHD-related difficulties perceived by patients, parents and physicians at various times of the day. Other scales available so far to assess the level of psychosocial functioning from several perspectives, such as the Child Health Questionnaire (CHQ) , Child Health and Illness Profile (CHIP) , or the Marburg System of Quality Assurance and Therapy Evaluation (MARSYS) [46, 47], do not distinguish between various times of the day. Furthermore, the GIPD can be taken to reflect the health-related quality of life in children and adolescents with ADHD . However, since the introduction of various long-acting ADHD medications, interest in duration of action of these medications over the day has increased . The GIPD was therefore designed both to capture ADHD-related difficulties and to distinguish between various times of the day. Thus, results obtained by using the GIPD can be compared with results obtained by using other instruments that distinguish between various times of the day, such as the Daily Parent Rating of Evening and Morning Behavior (DPREMB) scale  or the Weekly Rating of Evening and Morning Behavior (WREMB) scale . As the GIPD was designed as a global impression scale, all five items of the GIPD resemble the Clinical Global Impression (CGI) scale [28, 29] quite closely.
A total of 421 children and adolescents diagnosed with ADHD according to DSM-IV criteria were included in this analysis of data from two open-label studies. The mean age of the patients was 11.1 (SD 2.74) years, 338 (80.3%) were boys, 83 (19.7%) were girls.
One of the findings of the two studies on which the GIPD validation is based was a relatively high percentage of patients with the predominantly inattentive type of ADHD. One can only speculate about the reasons. Perhaps there was some sort of selection bias in these open-label studies towards patients with the inattentive type, particularly the study with adolescents. In the study with children, only 19.5% of patients were of the inattentive type, whilst considerable 45.9% were of the inattentive type in the study with adolescents. This obviously resulted in a proportion of 29.5% with the inattentive type in the pooled data (children and adolescents). One further reason could be the fact that the symptoms change as patients grow older: hyperactive or impulsive behaviour tends to decline, whilst inattentive symptoms tend to remain. This would explain the greater proportion of patients with the inattentive subtype in the study with adolescents compared to the study with children.
Although it is short (5 items), the GIPD scale rated by parents, physicians and patients has been shown to be internally consistent. For all items at least a moderate item-total correlation was found. Moreover, the scale has also shown good test-retest reliability over a period of two weeks for all three perspectives. The mean GIPD total scores (OC) generally showed a parallel course over time from all three rater perspectives (Figure 3). Parents rated ADHD-related difficulties at baseline as significantly less severe than physicians, but the parent and physician total scores converged as early as week 2 and the Cohen's kappa coefficients indicate a moderate agreement between parents' and physicians' ratings. However, the agreement between parents and physicians on the one hand and the patients on the other hand were quite low, as indicated by the kappa coefficients. Thus, adults seem to agree to a greater extent on the degree of perceived ADHD-related difficulties in the patients than the children and adolescents.
However, patients, parents and physicians perceived an improvement of ADHD-related difficulties over time. Compared to the parent and physician ratings, the children and adolescents perceived their difficulties as significantly less severe throughout the entire study. This suggests that children and adolescents perceive their ADHD-related difficulties to a lower extent than adults do. These findings reflect the findings from the two studies that assessed children and adolescents separately [25, 32]. Moreover, studies on the correlations between the ratings of behavioral and emotional problems as rated by parents and children or adolescents also reveal little agreement in the ratings of parents and their children. For example, Achenbach et al.  found in their meta-analysis a correlation of r = 0.25 between parents and children ratings of behavioral and emotional problems. This result was replicated in a German sample .
The higher correlation between parent and physician perspectives may also be due to the fact that the physicians based their ratings primarily on the information from the parents rather than the patients. Thus, convergent validity may be artificially inflated. However, the patient perspective on daily difficulties provides important additional information when evaluating the efficacy and effectiveness of a treatment. The low to moderate correlations of the different perspectives underline the need for assessing these perspectives separately.
The moderate correlations between physician-rated ADHD symptoms on the ADHD rating scale and the GIPD indicate a reasonable discriminant validity of the difficulties and the impairment of the child in different settings throughout the day as assessed by the GIPD scale on the one hand and the ADHD-RS on the other. Somewhat higher correlations were found with the WREMB-R which assesses a similar construct (i. e. 11 specific common morning or evening behaviors). This finding indicates the convergent validity of the GIPD in showing higher correlations to scales assessing similar constructs.
These studies and analyses have several limitations. Most importantly, they did not include a placebo control, so that the degree to which the results reflect drug-specific effects cannot be determined definitively. Also, sensitivity regarding differences between placebo and active comparator cannot be determined. In these studies, no further instrument assessing behavioral or emotional problems as perceived by the patients were used. Such self-report scales on ADHD symptoms or ADHD-related difficulties allow the calculation of convergent and discriminant validity and allow comparisons with other self report measures . A future comparison of this sample with children without ADHD or with other behavioral or emotional problems would be interesting. This would allow the assessment of perceived difficulties in a more representative sample. A further limitation of this study is the age-distribution of the sample that does not reflect the age-distribution of individuals with ADHD in the general population. This is due to the fact that this analysis is based on two identical studies, one in children and one in adolescents. Beyond age as a covariate, other factors such as ADHD subtype, co-morbid disorders, type of school, family environment or other environmental factors may also influence a range of GIPD results (e.g. agreement between perspectives or treatment response as reflected by the GIPD). Further research on these factors is warranted.
Treatment-emergent adverse events during the course of the two studies have been reported elsewhere [25, 32].
Overall, the GIPD can be considered an internally consistent, reliable and valid measure to assess difficulties experienced by children with ADHD throughout the day and can be used as an indicator for psychosocial impairment and quality of life . Moreover, the two treatment studies on which this analysis is based also show that the scale is sensitive to treatment-related change.