47 Translation and validation of the LORQv3 in Dutch 3 contacted and asked to participate through letters and telephone calls. Dentists who agreed to participate asked their patients to fill out the questionnaire. Participants completed the LORQv3-NL during their dental appointment. The internal consistency of a questionnaire relates to its homogeneity. All items should measure different aspects of the same trait. Therefore, different items should correlate moderately with each other and with the total score [9]. The internal consistency of the total LORQv3-NL, as well as its 2 sections, was assessed by calculating Cronbach α values. Values of 0.70 to 0.80 are considered satisfactory for a reliable comparison between groups. For clinical purposes, a minimum of 0.90 is required, while values of at least 0.95 are normally considered desirable [10]. However, according to Streiner [11], α values over 0.90 most likely indicate unnecessary redundancy rather than a desirable level of internal consistency when there are more than 20 or so items. A subsample of 34 participants received a second LORQv3-NL questionnaire and completed it during another dental appointment, or they received and returned a second questionnaire by mail. The interval between the first and second questionnaire was 2 weeks. This interval was selected because the measured variable was assumed not to have changed in this time, and participants were unlikely to remember their first response over this interval. The test-retest reliability of the LORQv3-NL and its 2 sections was determined by calculating the weighted kappa coefficient. Discriminative validity and convergent validity were used to measure construct validity. For convergent validity, the correlation between the questionnaire and other related measures was assessed. In this study, a subsample of 17 participants also filled out the OHIP-NL14, the Dutch version of the OHIP-14. A positive correlation between the 2 scores would indicate convergent validity. The LORQquestionnaire was originally designed for patients with head and neck cancer. To test discriminative validity, a group of 25 patients with head and neck cancer also filled out the LORQv3-NL. These patients were expected to have higher scores than the noncancer group because of their compromised oral environment as a result of surgery or radiotherapy [12, 13]. Furthermore, a difference can be expected between the patients visiting the university dental clinics and patients going to a general practitioner for routine examinations. We hypothesized that the patients visiting the university dental clinic actively reached out for help, so they would have more complaints and therefore demonstrate higher scores. The LORQv3-NL scores were compared among those 3 groups.
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