Questionnaires are frequently used instruments to collect data in epidemiological studies. In countries where more than one language is spoken, the development of a questionnaire in more than one language is needed. The objective of this study was to develop and test the repeatability and validity of English and French versions of a personal interview-format questionnaire designed to capture udder health related management practices used on dairy farms. A standardized protocol was used to develop and translate the research instrument. Equivalence of the English and French questionnaires was assessed using a cross-over study design with 24 bilingual dairy producers completing both versions on three different occasions in a randomly assigned sequence. Repeatability of the questionnaire was evaluated using the test-retest method with the same questions being asked on two different occasions to 88 dairy producers participating in the National Cohort of Dairy Farms of the Canadian Bovine Mastitis Research Network. Validity of the questions related to milking procedures and general housing was assessed using on-farm observations as a gold standard. Measures of agreement were calculated using kappa, quadratic-weighted Kappa and concordance correlation coefficients for categorical, ordinal and continuous variables, respectively. Sensitivity and specificity estimates were computed for the validity analysis. The overall equivalence of the English and French versions of the questionnaire was adequate; agreement measures when administered twice in the same language were not significantly higher than when administered in each language. Similarly, questionnaire overall repeatability was good. When accounting for prevalence bias, Kappa and CCC estimates ranged from 0.40 to 0.92 for 27 of the 29 items evaluated in the questionnaire, with 18 items yielding agreement estimates greater than 0.60. Finally, milking procedures and general housing questions validity was excellent with mean sensitivity and specificity of 86% and 92%, respectively. Although the overall evaluation of the instrument was satisfactory, specific doubtful items were identified. This illustrates the need to address questionnaire reliability as even rigorously designed and pre-tested questions can have poor repeatability or validity. Our results indicate that the developed English and French questionnaires can be used simultaneously to accurately measure the udder health related management practices used on Canadian dairy farms. This questionnaire is adaptable for use in other developed dairy industry populations. The questionnaire is freely available online at www.mastitisnetwork.org under the "Publications/others" section.
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