The K-KIDSCREEN-52 HRQOL was developed from the English KIDSCREEN-52, which was funded by the European KIDSCREEN group (9). It was translated into Korean according to international guidelines (13). The KIDSCREEN-52 generic HRQOL questionnaire was translated by a forward-backward-forward translation technique. In a first step two independently working psychiatrists translated the English Draft into the Korean language. Thus two different versions of translation were acquired (Forward Translation 1 and Forward Translation 2). In the following reconciliation step the two forward translators and one project member reviewed the respective two forward translations in order to create the respective Reconciled Forward Translation, meeting all demands of conceptual equivalence with the original English Draft. Afterwards the respective Reconciled Forward Translation was back translated into English by a third translator. In the next step two research members as well as the forward translator compared the respective Backward Translation with the Draft, thus reviewing the respective Reconciled Forward Translation and thereby generating the respective Final Forward Translation. Subsequent to the generation of the respective Final Forward Translation, all reviews and translation data was send to the German study center for documentation. The objective of the following telephone conference was to resolve inadequate concepts of translation as well as all discrepancies between alternative versions.

The KIDSCREEN-52 questionnaire consisted of 52 items assessing ten HRQOL dimensions (Table 1). It assessed either the frequency of behavior/feelings or intensity of an attitude. Both possible item formats use a 5-point Likert response scale, and the recall period is one week. Scores are computed for each dimension (i.e. items are equally weighted) and are transformed into T-values with a mean of 50 and a standard deviation of 10; higher scores indicate higher HRQOL and wellbeing (14).

All students from the seventh to ninth grade (age 13-15 yr) at one middle school in Seoul, Korea, were invited to take part in the study, provided that their understanding of the Korean language and their reading and writing skills were sufficient. The sample consisted of 405 adolescents, of which 204 were boys and 201 were girls. The mean age for the sample was 13.83 yr.

The students were told that the purpose of the study was to attain knowledge about the quality of life and health, in general, among teenagers. They were further informed that their responses would be treated anonymously and that there was no right or wrong answer. The scale instructions were given in written form, and the test was performed during school hours and lasted 30 to 40 min. The rights of all participants were safeguarded through informed consent and confidentiality.

To address the properties of the measure in terms of convergent and construct validity, several other measures were included, in addition to the K-KIDSCREEN-52 HRQOL. Convergent validity was assessed by comparison of K-KIDSCREEN-52 dimensions scores with the PedsQL™ 4.0, a known and validated questionnaire measuring similar concepts. The PedsQL™ 4.0 Generic Scales consists of an overall HRQoL scale, a 23-item Total Score, and eight-item Physical Health Summary subscale and a 15-item Psychosocial Health Summary subscale. The Psychosocial Health Summary subscale was further composed of a five-item Emotional Functioning subscale, a five-item Social Functioning subscale, and a five-item School Functioning subscale. The Physical Health Summary subscale was equivalent to and also referred to as the Physical Functioning subscale (15-17). We used the Korean version of the PedsQL™ 4.0. The internal consistency coefficient of the Korean version of the PedsQL™ 4.0 has been reported previously to be 0.93 (18). The Children's Depression Scale (CDI) (19, 20) and the Revised Children's Manifest Anxiety Scale (RCMAS) (21, 22), which have been widely used for self- report to measure depressive and anxiety symptoms, were included.

The statistical analyses for the reliability and validity of the K-KIDSCREEN were performed using SPSS for Windows (Version 10.0; SPSS, Chicago, IL, U.S.A.). The internal consistency of each subscale was estimated by using the Cronbach's alpha coefficient. Alpha coefficients of 0.7 or higher were considered acceptable. The test-retest reliability was estimated via a comparison of the scores achieved when add ministered on two separate occasions, at interval of one week. Pearson correlation coefficients were computed to analyze convergent validity between K-KIDSCREEN-52 dimensions and PedsQL™ 4.0, CDI, and RCMAS. Convergent validity was considered to be demonstrated when correlations between comparable dimensions were significantly higher than those between theoretically different dimensions and were of a reasonable magnitude. Correlation coefficients between 0.1 and 0.3 were considered low, those between 0.31 and 0.5 moderate, and those over 0.5 were considered high (9, 23).