Page 35 - THE PERCEPT STUDY Illness Perceptions in Physiotherapy Edwin de Raaij

Cross-cultural adaptation and measurment properties
Discussion
The Brief IPQ-DLV was adapted from the original English version IPQ-B. All stages for cross- cultural translation and adaptation recommended by Beaton et al. (2000) were sucessfully followed.
Results indicate that the Brief IPQ-DLV is easy to use, and takes less than 5 min for patients to complete and physiotherapists to score. Both first-grade students and individuals attending physiotherapy practice were able to understand and answer the questions of the IPQ-B-DLV. Therefore, it seems justified to conclude that the Brief IPQ-DLV is easy to understand. Howev- er, in a think aloud study conducted by van Oort et al. using this questionnaire several prob- lems were identified29. Especially the control item gave rise to misinterpretations indicating that there is a need to pay greater attention to interpretation and comprehension of the IPQ items by patients. Future studies need to address these issues of interpretation and need to establish responsiveness of this questionnaire.
Assessment of the reproducibility showed moderate to good reliability in a time interval of 1 week. The Consequences, Concern, and Emotional Response dimensions reached the predetermined goal of Kw >0.7026. The other dimensions showed moderate reliability coefficients between 0.51 and 0.68. To our knowledge this study is the only one, which assessed reliability with Kw statistics. Therefore comparison with earlier studies cannot be made. The original study of the Brief IPQ used the Pearson’s r4. This is in our opinion not the most appropriate statistic for reliability because systematic differences are not taken into account26.
Questions by which illness perceptions were assessed can be seen as a measurement involving judgment using idiosyncratic criteria24. This means there is a chance that response shift phenomena could play a role in the reliability assessment of the Brief IPQ-DLV. It is not known whether patients interpret an illness perception question equally at two different moments in time. When interpreting reliability coefficients of the Brief IPQ-DLV, this idiosyncratic issue must be considered.
The SDC, as part of agreement, of the Brief IPQ-DLV is an important measurement property that can be used in intervention studies concerning Illness Perceptions. If in an intervention study the outcome on a Brief IPQ-DLV dimension extends the SDC it is an indication for a ‘real’ change in illness perception following the intervention. The SDC for individual evaluation purposes for five Brief IPQ-DLV dimensions was less than three points. This means that a
33
2