52 Chapter 3 Discussion The results from this study support the rejection of the first null hypothesis, as the LORQv3-NL identified differences among the data from patients visiting general practices, patients visiting the university dental clinic, and patients with head and neck cancer. The second null hypothesis was retained, as the LORQv3-NL could not identify differences between test-retest data at an interval of 2 weeks. This study describes the translation, cultural adaptation, and validation of the LORQ into Dutch settings. To achieve a comparable version of an instrument to be used in a new country and culture, a cross-cultural adaptation of the instrument is necessary. A cross-cultural adaptation involves both linguistic translation and cultural adaptation to maintain the content validity of the instrument at a conceptual level across different cultures [8, 14]. The reliability and validity of the Dutch version of the LORQ were assessed to decide whether it could be recommended as a reliable and discriminating questionnaire. The LORQv3-NL showed good psychometric properties. The general internal consistency of the LORQv3-NL can be considered satisfactory and comparable with the original version. In general, the Cronbach α value of the Dutch version was slightly lower than the original English version. This might be due to the group size or the group composition. The English version has been tested mostly on patients with head and neck cancer. Their responses are probably more divergent than a general practice group, because in general they have more complaints. A few items showed a low correlation with the total. Items 11 through 14 deal with esthetics and express how much the patient feels disturbed by his or her appearance. The rest of the questionnaire focuses more on other functional aspects such as mastication, swallowing, and pain. This might explain the lower item-total correlation of these questions. Items 29 and 37 ask whether, during eating, the patient has ever removed his or her maxillary or mandibular denture. These questions are very specific and might not relate to pain or lack of masticatory ability directly, leading to low item-total correlations. For a few items, the item-total correlation was high (highest was 0.76 for item 34). This might suggest that these items are redundant. The original LORQv3 questionnaire formed the basis for this translation. To keep the LORQv3-NL comparable with the original questionnaire LORQv3, no items were deleted despite the possibility of some items being redundant.
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