Population norms and cut-off-points for suboptimal health related quality of life in two generic measures for adolescents: the Spanish VSP-A and KINDL-R

Background: Health-related quality of life (HRQL) outcome measures are complex and for further application in clinical practice and health service research the meaning of their scorings should be studied in depth. The aim of this study was to increase the interpretability of the Spanish VSP-A and KINDL-R scores. Methods: A representative sample of adolescents aged 12 to 18 years old was selected in Spain. The Spanish VSP-A and KINDL-R, two generic HRQL measures (range: 0-100), were self-administered along with other external anchor measures (Strengths and Difficulties Questionnaire, Oslo Social Support Scale and self-declaration of chronic conditions) and sent by post. Percentiles of both HRQL questionnaires were obtained by gender, and age group and effect sizes (ES) were calculated. Receiver Operating Characteristic curves and related sensitivity (SE) and specificity (SP) values were also computed. Results: The Spanish VSP-A and KINDL-R were completed by 555 adolescents. A moderate ES was shown in Psychological well-being between younger and older girls (ES: 0.77) in the VSP-A and small ES in the KINDL (ES: 0.41) between these groups. A SE and SP value close to 0.70 was associated to a global HRQL score of 65 in the VSP-A and 70 in the KINDL-R, when compared to anchors measuring mental and psychosocial health. Adolescents with scores bellow these cut-off points showed a moderate probability of presenting more impairment in their HRQL. Conclusion: The results of this study will be of help to interpret the VSP-A AND KINDL-R questionnaires by comparing with the general population and also provide cut-off points to define adolescents with health problems.