The evaluation of the sub-scales of the KIDSCREEN-27 and KIDSCREEN-52, respectively, is done analogously to the description for the KIDSCREEN-10. You will find more information related to the differences between the three versions of the questionnaire at the end of the page.
Please note: However, 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.
STEP 1: ITEM RECODING
For most items, a higher score reflects higher health-related quality of life (HRQoL). This means that they are positively worded and consistent with the scoring (assigned value of a response option). However, some items are worded negatively. These must be recoded so that higher scores represent higher health-related quality of life. That is, a score of 1 becomes 5, 2 becomes 4, 3 remains 3, 4 becomes 2, 5 becomes 1.
The items in question have already been recoded in the Excel table below.
Important Note: The recoding of the negatively worded items must be carried out regardless of which of the two evalu-ation procedures you choose.
Procedure: At the beginning of the evaluation process, assign the numbers given in the table below to the selected answer options (for each item, i.e., for each question). For example, if the answer option "not at all" was selected for the first item, this corresponds to a numerical value of "1". Items 3 and 4 of the table are already recoded, i.e. if the answer option "very often" was selected, this corresponds to a numerical value of "2".
Example: In response to the question "Did you feel fit and well?", the child answered "quite a bit". The item coding for this is 4. To the question "Have you been full of energy?", the child answered "Often". Here, the item coding is also 4. To the question "Have you felt sad?", the child answered "Never." Since this is a negatively-worded item, the coding here is 5. In this way, you can convert the text responses into item codes and then move on to the second step.
STEP 2: CALCULATION OF THE SCALE SUM SCORE
In the next step, add up the values of all* items (item scores) of the scale to obtain a scale sum score. This gives you a value between 10 and 50, where 10 represents the lowest possible value and thus a very low health-related quality of life and 50 the maximum value, i.e. a very high health-related quality of life.
*(of all 10 index items; the additional item for general health should not be included!)
Important Note no. 1: The sum score may only be calculated "by hand" if ALL items have been answered. Items that have not been answered may not simply be recalculated. Thus, the total sum score of the scale should not be calculated by imputing the missing values. However, if there is no more than one missing value, it is possible to use the SPSS syntax to calculate the Rasch person parameter based on the existing item responses. For the "by hand" calculation, we therefore assume completely answered questionnaires (no missing values).
Important Note no. 2: To calculate the scale sum score for the item KYPHY, the item KY(27/52*)PHY1 (*depending on the questionnaire version) must be recoded:
1 to 2 becomes 1; 3 to 4 becomes 2; 5 becomes 3.
Then KYPHY 1 must be recoded into KYPHYc (according to the SPSS syntax) – thus the calculation has to be done as follows: KYPHYc + KYPHY 2 + KYPHY 3 + KYPHY 4 + KYPHY 5.
STEP 3: RASH PERSONAL PARAMETERS and T-VALUE STANDARDIZATION
The KIDSCREEN-10 was developed using the Rasch model. As part of the analyses according to the Rasch model, the so-called "person parameters" are estimated on the basis of the item responses. This was done with the help of the nor-malization sample. In this process, a Rasch person parameter is assigned to each possible scale sum score of 10-50. See the Excel spreadsheet below for an overview.
Unlike the ordinal scale sum score, the person parameter has the favorable property of being interval scaled. For easier interpretation of the results, the person parameters are z-standardized and converted to T-value norms, which are also listed in the table below. For the norm sample, the mean is fixed at 50 and the standard deviation is ±10. A higher T-value represents a higher health-related quality of life and a lower T-value a lower one.
Note: Here we present the norm values for the international sample. You can also use national norm values for the normalization or the classification of the results (see STEP 4). Please consult the Manual and the corresponding Manual Appendices.
Example: If a person has a sum score of 36 in the self-report, this corresponds to the Rasch person parameter 0.52 and thus a T-value of 43.35.
STEP 4: INTERPRETATION OF T-VALUES
Finally, to interpret the T-values, you can refer to the norm data tables. These can be found in the [LINK:] Manual Appendices A7_A-E. These norm data allow you to classify a person and their individual values, both in national and European comparison (comparison with the reference group). These are based on the data from the international sample of the KIDSCREEN project from twelve European countries. In principle, values below the threshold indicate a comparatively low health-related quality of life, while values above the threshold indicate a comparatively high quality of life.
Important: In general, the KIDSCREEN is not a clinical instrument, which is why there is no distinction between "healthy" and "sick". However, for interpretation purposes, the test values determined are classified as "normal" and "conspicuous".
Example: To classify the T-value of 43.35 in the example above, you can refer to the European norm data from Appendix A7-A. There you will find various comparison groups that you can use depending on age and gender. Assuming that the value 43.35 comes from a 9-year-old girl, the comparison value of the KIDSCREEN-10 is a mean value (Mean) of 53.82 with a standard deviation (sd) of 10.80. Thus, this value represents a somewhat low health-related quality of life in comparison with the normalization sample, but is still within the range of one standard deviation and can thus be classified as "average".
ADDITIONAL INTERPRETATION OPTION VIA THE T-SCORE MAP
In the case of items with several response categories, the so-called item threshold parameters, whose mean value rep-resents the average item difficulty, are also estimated in the course of model testing. These threshold parameters mark the intersections of two adjacent response categories and in principle divide the recorded construct into sections in which one response category has the highest probability. This is illustrated in the figure below. The tables for this can be found under Manual Appendices A8
EVALUATION OF THE KIDSCREEN-27 AND -52
The evaluation of the longer KIDSCREEN versions is analogous to the KIDSCREEN-10, with the special difference being that in addition to the total sum value, sum values of the sub-scales can also be calculated. Which items belong to which sub-scales can also be found in the Excel tables.
Example: You want to calculate the sum score of the sub-scale "Bullying" in KIDSCREEN-52. The three items of this sub-scale are marked with the abbreviation "BUL" in the Excel tables (see first table sheet with notes). All three items are worded negatively, so the answers must be assigned to the corresponding codes in such a way that higher values in turn mean a higher quality of life. If the child answered "seldom" to all three questions, the summed value is (4 + 4 + 4 =) 12. Using the norm table, you can see that this value corresponds to a Rasch person parameter of 0.81 and a T-value of 38.29. In the Manual Appendices A7_A-E you will then find the corresponding norm values. For comparison, girls aged 8-11 have an average score of 47.53 with a standard deviation of 10.65. The sum score is thus below the standard value but within one standard deviation and is thus still within the "average" range.