title: Health-related quality of life instruments and individual diagnosis - a new area of application.
abstract: OBJECTIVE
  Various health-related quality of life (HRQoL) instruments for children and adolescents have been developed and are applied in clinical and health economic studies with the research focus on the HRQoL of specific groups of responders, comparing these groups respectively. However, if HRQoL assessment aims to contribute on deciding upon a suitable individual treatment and the evaluation thereof, as well as to identify hidden morbidities, an individual diagnostic perspective is required.To date, the majority of HRQoL questionnaires for children and adolescents are not designed for individual diagnostic assessment and comparison. This paper aims to demonstrate that should a particular measurement tool meet specific psychometric requirements - an individual diagnostic assessment on mental health related problems is possible. We investigated whether or not the KIDSCREEN-27 HRQoL instrument for children and adolescents is able to detect mental health problems in general, provided we apply a principal component analysis (PCA) for summative scaling.
  
  
  METHODS
  The cross-sectional survey of the KIDSCREEN project was carried out in 13 European countries (AT, CH, CZ, DE, EL, ES, FR, HU, IE, NL, PL, SE, UK). The Rasch-scaled KIDSCREEN-27 test-data of 22,830 children and adolescents were analysed. To achieve a summative scaling PCA was performed on the correlation between the KIDSCREEN-27 scores. The principal component (PC) values were estimated and used to score the respondents. The reliability and diagnostic quality of this scoring was examined.
  
  
  RESULTS
  The first PC accounted for 58.28% of the entire variance within the KIDSCREEN-27 scores. All KIDSCREEN scales loaded high on the first PC. The reliability of the linear combination of KIDSCREEN-27 scores with the PC-values was rr=.94 and thus above the threshold for individual comparison. This value was higher than the values for the original single KIDSCREEN-27 scores (rr=.78-.84). The receiver operating characteristic curve (ROC) was calculated whilst screening for respondents with a mental health problem in general (Strengths and Difficulties Questionnaire). The area under the ROC (AuC) was .80 and statistically significant lower than the AuC issued after a logistic regression analysis employing the 5 original KIDSCREEN-27 scores (AuC=.83). However, according to international conventions, both AuCs denote a "good" discrimination.
  
  
  CONCLUSIONS
  Specifically for the KIDSCREEN-27 the results show that the application of a specific scoring algorithm leads to fulfil pre-specified demands of high reliability. The applied scoring approach leads to a good discrimination of the measurement, thus enabling to detect a mental health problem in general using the HRQoL test-data. The presented approach can enhance the usability and range of application of HRQoL measurement.
authors.affiliation: Research Unit Psychosocial Health, Robert Koch-Institute, Berlin, Germany Department of Medical Psychology, Center of Psychosocial Medicine, University Hospital Hamburg-Eppendorf, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Erhart
authors.forename: Ulrike
authors.initials: U
authors.lastname: Ravens-Sieberer