The impact of a treatment significantly relies on the generalisation of treatment effects, which can be conceptualised as occurring across settings, behaviour variables and time [19
]. This underlines the necessity to consider multiple indicators as well as to assess follow-up measurements concerning the stability of effects. In previous papers, we reported the immediate treatment effects of a NF training (theta/beta training and SCP training) compared to an AST on different outcome levels, encompassing behavioural and neurophysiological measures [12
]. This paper deals with the 6-month follow-up analyses of the behavioural outcome. Since some children started medication, we conducted a per-protocol analysis in order to avoid confounding the treatment effect with medication effect. For 61 of the 94 children (ca. 65%) of this sample, 6-month follow-up data (parent ratings) could be analysed. On average, effects were sustained at follow-up and the effects in the NF group were still superior to those of the control group. For the total score of the German ADHD rating scale (primary outcome measure), a medium effect size was obtained. Further, effects were not restricted to core ADHD symptoms but could also be observed in other domains (homework situation, conduct disorder; small to medium effect sizes). Regarding order effects for the NF protocols, the tendency for larger improvements when theta/beta training preceded SCP training could not be confirmed in the follow-up sample.
Since settings and demands for NF and the control training were comparable, these findings indicate that mainly specific effects accounted for the superiority of NF compared to the ASTs.
Specificity of effects is further supported by associations between neurophysiological patterns and the outcome at the clinical (behavioural) level as reported in [13
]. For example, in theta/beta training, the decrease of theta activity in the resting EEG was associated with a decrease of the FBB-HKS total score [13
]. Concerning SCP training, children with a higher CNV in an attention test at baseline showed larger improvements after the relatively short training block [32
On the other hand, partly due to the non-blind design, it cannot be ruled out that unspecific effects might have also contributed to the behavioural effects.5
There was a relatively large number of dropouts, i.e., children who either started a medication or for whom no questionnaires were received, at follow-up (about 35%). However, dropouts were not characterised by a worse training outcome at the end of the training. These children (mainly in the control group) had slightly (but non-significantly) higher scores on the German ADHD rating scale already at the beginning of the training. In general, children for whom follow-up data were available could not be differentiated from dropouts with respect to behavioural or demographic characteristics. So, it seems unlikely that the follow-up results were strongly biased by the large portion of dropouts.
Findings are based on parent ratings only. At the post-training assessment, for only about 70% of the children, ratings of the same teacher who had completed the pre-training questionnaires were available. Expecting further high dropout rates due to change of teachers and loss of motivation to complete the questionnaires, we decided not to include teacher ratings in the follow-up analysis. It can be questioned whether teacher ratings would have supported the follow-up results obtained from parent ratings. However, in [17
], parent and teacher ratings did not develop differentially from post-training to follow-up. In our study, comparable effects resulted for parent and teacher ratings at the post-training assessment [12
50% of the children completing the training were categorised as non-responders, according to a criterion of 25% reduction in the primary outcome measure. 11 out of 59 children of the NF group started a medication during the follow-up interval. Our study was not designed to achieve maximum NF training effects but had an arguably artificial scientific setting (e.g., separating theta/beta and SCP training in two separate, non-coordinated blocks). Nevertheless, the low responder rate and the portion of children starting a medication in our study argue against NF as a stand-alone intervention for children with ADHD. The results indicate that not every child with ADHD may improve after NF treatment. In our opinion, NF should rather be seen as a treatment module for children with ADHD which can be embedded in a multimodal treatment program tailored to the individual needs of a child.
Stability of training effects at follow-up refers to the mean scores of the NF group and naturally does not apply to all individuals within the group. In our design, we used a fixed number of training sessions. This was intended to standardise number of treatment sessions across all individuals. However, qualitative analyses of our data suggest that children vary in their abilities and speed to learn and apply NF techniques. One block of 18 units for a single protocol might have been too short at least in some children to build up stable regulation capability and to establish transfer into daily life sufficiently. Further research therefore would be required to determine the optimal NF protocol (or combination of protocols) and the adequate number of treatment sessions for a particular child.
Coming back to the long-term outcome, it could be helpful at least for some of the children to conduct further training sessions with longer intervals between the training session to sustain and consolidate regulation capabilities and the transfer into daily life, just as it is usually practiced in conventional cognitive-behaviour therapy. In this respect, the possible benefit of such booster sessions should also be investigated in further studies.