For more detailed questions, we recommend that you contact a statistics consultant at your institution or attend a seminar/online training for SPSS. Please understand that we cannot answer every question, especially if it is specific to your study.
Systematic Missing Values (KIDSCREEN-10)
The syntax for calculating the T-values for the KIDSCREEN-10, allows at most one missing value. Therefore, this syntax cannot be used if more than one item is systematically missing in samples (e.g., because individual subject areas, such as school, are not applicable). The only option left to researchers who still want to use the KID-SCREEN-10 is to calculate an index score based on the items that can be evaluated. However, this procedure should definitely be discussed as a limitation. Furthermore, a direct comparison with other studies that have per-formed an evaluation according to the manual is not possible.
Missing Values for Proxy Questionnaires
Only one syntax was created, for missing values in self-reports of children, but not for proxy-reports. Attempts have already been made to reproduce this existing syntax and adapt it for parents; however, this has not yet been pos-sible.
Meaning of “Transformed to 0-100” Scales
The transformation of scales to 0-100 offers the possibility to compare different scales. Thus, results of the KID-SCREEN can be compared with other scales transformed to 0-100.
Total Score for KIDSCREEN-52 and KIDSCREEN-27
There are no total scores for the KIDSCREEN-52 and KIDSCREEN-27. For these questionnaires, the different scales are always calculated. Only the KIDSCREEN-10 results in a total index score formed from all 10 items.
Calculation of Sum Scores instead of T-Values
It is possible to calculate sum scores instead of T-scores for the KIDSCREEN. However, by calculating T-values, comparison to norm data and other studies is possible. For the calculation of sum scores there are no syntaxes available.
The group values of a study group can be compared with the values of the reference population. Specific refer-ence values are available for different countries, by gender and for two different age groups. Values within a defined range around the reference limit can be considered average. Groups with a higher value can be assumed to have a high health-related quality of life (HRQoL). Groups with lower values can be assumed to have a low HRQoL. In groups with low HRQoL, the specific reasons for these low values should be investigated.
Thresholds to classify results as "normal" or "abnormal" can be calculated by "reference value +/- ½ standard de-viation". The reasons for this calculation are statistical considerations: The range "reference value +/- ½ standard deviation" covers 38% of the sample in a normally distributed sample and 31% each are above or below this range.
In general, the KIDSCREEN is not a clinical instrument, so there are no cut-off values between "healthy" and "sick" or similar. Cut-off values should always be set with regard to the research question and in accordance with exist-ing literature.
Comparisons over Time
If results are to be compared over a period of time, both raw values and transformed scales or even T-values can be used, since the conversion for the scales is always applied in the same way. Thus, results are not changed and remain comparable.
Significant Changes over Time
It is problematic to speak of "clinically significant differences", since there is no explicit diagnosis behind health-related quality of life. With T-scores <40 we can assume a low quality of life, while with T-scores >60, a high quality of life can be assumed.
If the participants are to be divided into groups, the standard deviation (SD) can be used. However, whether a deviation by a full SD or even half an SD is meaningful, must be weighed up on the basis of the relevant literature.
Consistency of the self and parent report
Regarding the proxy problem, i.e. the comparison of data collected from children and adolescents with the data provided by their parents, we recommend the following publications from the field of "Quality of life":