66 Chapter 4 for construct validity was already calculated by Bruinewoud et al.5 and showed good correlation between the individual items. For multi-item measurement instruments based on a formative model that applies to the complaint items in our model, there are no well-known measurement theories (a framework for model of the instrument can either be reflective or formative)6. Therefore, the development of multi-item instruments following a formative model is merely based on common sense of experts in the field rather than on statistical procedures.6 Reliability was defined as ‘the degree to which the measurement is free from measurement error’.7 In the same paper Mokkink et al provided an extended definition of reliability: the extent to which scores for patients who have not changed are the same for repeated measurement under several conditions, for example using different sets of items from the same multi-item measurement instrument (internal consistency) and over time (test-retest).7 Internal consistency of the OQUA was already tested by Bruinewoud et al (2018).5 The aim of this study was to investigate construct validity, test-retest reliability and responsiveness of the generic Otology Questionnaire Amsterdam. The OQUA was expected to show good construct validity, good test-retest reliability and if compared to a similar questionnaire like the Glasgow Health Status Inventory (GHSI) or a Global Rating Scale (GRS) to show good responsiveness. Material and Methods The evaluation of OQUA’s psychometric properties was performed following ‘a practical guide to biostatistics and epidemiology for measurements in medicine’ of de Vet et al.6 and the COSMIN checklist8. The validation, reliability and responsiveness was done using the 2018 version of the OQUA, in chapter 3 on page 48-49 of this thesis. The original Dutch version of the OQUA can be found at the end of this thesis. All analysis were done using IBM SPSS Statistics version 22. Ethical considerations The study protocol, including the development of the OQUA, was assessed by the Medical Ethics Review Committee of Amsterdam UMC, VU University Medical Centre, which led to the decision that the Medical Research Involving Human Subjects Act did not apply to this study. Written informed consent was obtained prior to study participation. All data from submitted questionnaires was completely anonymised.
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