we retrieved the datasets of our original validation studies and computed the average scores of hvs and non - hvs subjects [ 2 , 4 ] . for the first validation study they were all patients from a psychiatric or internal medicine outpatient clinic or a lung function laboratory . patients who experienced their main complaints after voluntary hyperventilation were compared to patients who did not . in the second validation study , a group of physician - diagnosed , nonasthmatic hyperventilators were compared to nonasthmatic normal controls . figure 1 shows that the hyperventilators score equally highly on the nijmegen questionnaire in both studies but the controls were patients in the first study ( nijmegen questionnaire score 19.510.5 ) and normal subjects in the second ( nijmegen questionnaire score 11.95.5 ) . the cut - off point for optimal differentiation appeared to be a sum score of > 22 in the first study . in the second study , we calculated percentages to correct classification for different values of the sum score . we shuffled across possible cut - off points and found percentages correctly classified at > 17 ( 90.6% ) , > 18 ( 94% ) and > 19 ( 92.6% ) . it shows that these complaints  are not part of the minor disturbances that commonly occur  and are not  part of normal life  . figure  1nijmegen questionnaire ( nq ) scores ( meansd ) of hyper- ventilation syndrome ( hvs ) and non - hvs subjects in two validation studies . nijmegen questionnaire ( nq ) scores ( meansd ) of hyper- ventilation syndrome ( hvs ) and non - hvs subjects in two validation studies . complaints from anxiety disorder or other stress- or anxiety - related problems , nor has this been done in later studies . both studies basically offer evidence that an elevated nijmegen questionnaire score is  abnormal  . the nijmegen questionnaire is therefore a valid screening tool to detect patients across several medical specialties for whom the complaints may not be ( fully ) due to physiological abnormality . most studies in clinical medicine , like pulmonology or otorhinolaryngology , do indeed use the nijmegen questionnaire to detect patients for whom something other than the medical condition may be a cause of the complaints and , thus , medical treatment should be reconsidered . used the nijmegen questionnaire as a screening test for nasal congestion in an otorhinolaryngology clinic and found 28 out of 118 patients to have elevated scores . in 12 of the 28 patients , the original diagnosis was reconsidered they commented that the major benefit is  that a patient is spared an unnecessary and unhelpful procedure and the overall success of surgery is improved through better patient selection  . this corresponds with a major motivation in the first report on hvs , that  early detection of these tension related complaints would prevent unnecessary visits to medical specialists and treatment  . the validity and cut - off score of the nijmegen questionnaire to detect  abnormality  depends on a comparison with normal values in the same setting and culture in which the questionnaire is used . normal values were found in several studies in english , belgian and dutch subjects [ 68 ] and range from 10127 . . inspection of the 16 items of the nijmegen questionnaire indicates that the sum score is related to stress , respiration and anxiety . they overlap with symptoms of panic disorder but only a subgroup of patients with high scores on the nijmegen questionnaire have been actually diagnosed as having panic disorder . many asthmatics have an elevated nijmegen questionnaire score [ 9 , 10 ] , which corresponds with poor asthma control [ 9 , 11 ] . the relationship with hypocapnia is variable and often too weak to call the nijmegen questionnaire score a measure of hyperventilation [ 9 , 13 ] . thus , we prefer to describe the nijmegen questionnaire score a measure of  functional respiratory complaints  . the word respiratory refers to ventilation , dyspnoea and breathing movement ; the word functional refers to the relationship with stress and anxiety . in the pioneering article by thomas 
 et al . , the term this introduced the concept that breathing may be functionally disturbed beyond and even without hypocapnia . this wider concept of dysfunctional breathing is possibly the reason for the increasing popularity of studying it , but at the same time raises the question of its definition and measurement [ 14 , 15 ] . it is important to realise that breathing has several global functions , each of which can become dysfunctional [ 13 , 16 ] . firstly , breathing has the function of air transport and diffusion ( lung function ) . secondly , the process of expansion and contraction of the trunk not only serves as the  air pump  but has also an important function in posture and movement ( biomechanical function ) . thirdly , the subjective experience of breathing is an important contributor to the  sense of self thus , the lack of clarity over dysfunctional breathing is realistic when taking the multidimensionality of breathing into account . multicomponent assessment is required . in the clinical evaluation of the presence of dysfunctional breathing , therefore , objective criteria , derived from the somatic functions of breathing , play an important role [ 9 , 20 ] . it seems desirable , therefore , to use at least two kinds of criteria , subjective and objective , to assess dysfunctional breathing . the nijmegen questionnaire mainly reflects the subjective , psychic dimension of breathing and its response to stress . one original intention of the nijmegen questionnaire was to have a tool to evaluate whether subjects with high scores would benefit from breathing regulation . there are many forms of breathing regulation and there is , at present , no evidence for any particular approach . however , it probably involves rather intense education and training to reverse the abnormal pattern and improve proper  use  of the body . for instance , holloway and west   guided asthmatics , in five individual sessions , to re - educate them towards relaxed posture and breathing habits . afterwards , nijmegen questionnaire values normalised completely to an average value of 12 . first , on average , asthmatics do not have to have elevated nijmegen questionnaire scores . secondly , when breathing regulation is able to solve the problem that caused the high nijmegen questionnaire score , the score does indeed normalise to around 12 . in other studies of individual breathing regulation of patients without comorbidity , normalisation of nijmegen questionnaire values post - treatment was also found [ 12 , 22 ] . by contrast , simple breathing instructions from self - help manuals do not have any effect . evaluation of treatment by the nijmegen questionnaire is useful in clinical decisions at the individual level . subjects whose scores remain elevated or in the upper - normal range after adequate breathing regulation treatment deserve further attention to seek out the reason for the lack of normalisation . there could be a hidden lung function disturbance , persistent anxious cognitions , persistent stressful life situation or any other reason , which needs to be addressed in another way than continuing breathing regulation . for instance , han 
 et al .   studied 92 patients suspected with  hyperventilation complaints they received breathing regulation and , afterwards , showed a significant average decrease in nijmegen questionnaire score , but did not normalise . stratified by subjective benefit , however , only one third reported strong improvement in their complaints and their nijmegen questionnaire scores normalised to 9.4 . for the others , breathing regulation helped a little or not at all and their nijmegen questionnaire scores remained elevated . it is commendable , therefore , to evaluate treatment outcome not only by average reduction in the nijmegen questionnaire score , but to also stratify changes in the score according to improvement in the main complaint . in clinical studies that use the nijmegen questionnaire as a screening tool for dysfunctional breathing given the multidimensionality of breathing , a single criterion for establishing dysfunctional breathing is not sufficient : multicomponent assessment is recommended . this includes ventilatory parameters such as carbon dioxide tension , breathing movement parameters and subjective variables .
the nijmegen questionnaire was introduced over 30  years ago as a screening tool to detect patients with hyperventilation complaints that could benefit from breathing regulation through capnographic feedback [ 1 ] . 
 it was validated against the hyperventilation provocation test [ 2 ] , on the assumption at the time that hypocapnia was causally related to complaints . in later studies , 
 the correlation between nijmegen questionnaire scores and carbon dioxide tensions appeared highly variable . 
 the diagnosis of hyperventilation syndrome ( hvs ) was questioned and slowly disappeared . 
 nevertheless , the nijmegen questionnaire has remained in use and we have noticed even a recent increase in studies in clinical medicine as well as requests for permission to use the nijmegen questionnaire in new studies . 
 we would like to formally declare here that the nijmegen questionnaire is not copyrighted and is free to use . 
 it has been or will be translated , as far as we know , into greek , farsi , finnish , norwegian , swedish , spanish , filipino and chinese . however , the validity of the nijmegen questionnaire is often a point of discussion and we would like to make a few comments on that issue [ 3 ] .