Discussion
headaches, pain, headache, neck pain, head and neck injuries, Trauma, trauma
MINOR, DAILY HEADACHES
The results of the confirmative part of our investigation do not indicate that any of the candidate variables by themselves modify the effect of chiropractic treatment to a relevant degree. The observed treatment effects at selected anchor points ranged roughly from 0 to twice the observed overall effect, and probably mainly reflect random variation. This can be interpreted as a sign that chiropractic manipulation is offering an advantage for a broad range of children.The results of the exploratory part suggest that there may be still a potential to identify subgroups of children with little benefit from chiropractic treatment or with a more pronounced benefit, respectively. However, we must have in mind that the differences observed are probably too optimistic as the same data set was used to construct the index and to evaluate it. Hence, the clinical relevance of this finding remains unclear unless future studies can corroborate these findings. Nevertheless, it might still be of interest to take a closer look at the variables which might be predictive of the benefit from chiropractic treatment.The new index constructed included seven of the candidate variables. Three of them were already used by the principal investigator when representing her expectations of the highest and the lowest chance of a favorable outcome under chiropractic treatment: Frequency of headache, sport activity, and trauma experience. This can be seen as in concordance with the PIs experience. However, whereas we a priori regarded daily headache as an unfavorable condition for a benefit from chiropractic treatment, our analyses suggest an increasing benefit with increasing frequency. Such discrepancies with respect to the expected direction of the effect modification of single variables also explain the failure of the predefined expected benefit index to predict treatment effects. When correlating the five variables included in the index with the treatment effect on GPE, only trauma experience, screen time, and sport activity showed an association in the expected direction, whereas frequency of headache and age showed associations in the opposite direction.If there are any subgroups of children benefitting from chiropractic treatment to a higher degree than other children, our results suggest that besides headache characteristics such as frequency and intensity, social factors may play a role: short sleep duration, low socio-economic status, and headache within the family may predict a higher benefit from chiropractic treatment. However, these relationships were not consistently observed over the two outcomes. This should be investigated further in future research considering that more than 70% of children with recurrent headaches have a family member with headache, predominantly the mother [Sport activity and a history of neck pain may be predictive for a higher benefit from chiropractic treatment, but this was only observed for the outcome of GPE. Trauma was also included in the new index resulting from the exploratory analysis, although only demonstrating minor modifying effect by itself. The measurement of trauma in the present study was rather superficial and future attention should be increased because headache symptoms after minor head and neck injuries may be delayed for months or years after the injury [A basic limitation of our investigation is the sample size of the RCT. The sample size was chosen to establish an overall intervention effect. This implies a limited power to detect intervention effect modifiers. Furthermore, there have been no prior studies investigating effect modification in children with headache receiving chiropractic manipulation or sham manipulation. Consequently, we were forced to consider a rather broad spectrum of potential factors identified previously as important characteristic of different headache types or as potential risk factors. In addition, we rely on self-reports, which may only partially reflect the intended labeling. For example, according to the experience of the PI, some children might not report neck (or back) problems, although present, possibly because they have had it for so long that they consider it to be “normal”, or because the problems do not cause pain at the present time. In interpreting any observed effect modification, it must also be taken into account that the treatment provider was not blinded for the candidate variables. Thus, an estimated difference could be due to a more or less successful adaptation of the treatment to patient characteristics with respect to duration and intensity of the treatment.Finally, it should be noted that the PI often expressed the expectation that chiropractic treatment shows a 