The CRS-PRO is owned and copyrighted by, and the intellectual property of, Bruce K. Tan, MD, MS. Permission was obtained to use the CRS-PRO questionnaire from the development team. All patients who participated in the development gave their consent before participating in this study, which was carried out in accordance with the Declaration of Helsinki. All data were anonymized, and no identifying data were stored. The source language (original language in which the questionnaire was developed) was U.S. English. The target language (foreign language in which the questionnaire needed to be translated) was French. The CRS-PRO questionnaire was translated according to the recommendations of the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) [8]. Two professional translators, who were native speakers of the source language and bilingual in the target language were recruited, as were QoL experts in the target language. Three rhinologists in the target language were also involved. The three-step procedure translation process was as follows:

Step 1 (Forward translation): Three independent rhinologists produced a forward translation from the source language (English) into the target language (French). All were native speakers of French and spoke English fluently. They all discussed the translations and agreed upon a single reconciled version (the combined version). The aim was to achieve a conceptually equivalent translation of the original questionnaire; the language used had to be colloquial and easy to understand. By combining the three translations, we obtained French version 1.

Step 2 (Backward translation): French version 1 was translated into English by two native speakers of English who spoke French fluently. Indeed, this step requires a native speaker of the source language and bilingual in the target language who had no access to the original source version of the questionnaire. Items containing discrepancies were re-translated. Backward translation and a report of the translation were submitted to Dr. Tan for review and comment. This version was compared with the original CRS-PRO questionnaire and revised until a satisfactory translation was produced. Comparison of the backward version was made with the original source version to detect any misunderstandings, mistranslations, or inaccuracies in the intermediary forward version of the questionnaire. The development of a consensus and the translation by means of this committee methodology reduced the cultural and social bias that may result when only one or two translators are responsible for the translation. We thus obtained French version 2. This version was submitted to a panel of six health care professionals (5 ORL and 1 pneumologist) and 3 patients to determine whether it was understandable and easy to use. Further corrections led to the production of French version 3.

Step 3 (Patient testing): French version 3 was tested on 30 patients in 3 different French regions through face-to-face interviews, to determine whether instructions, filling method and items were understandable and unambiguous (men and women). Patients were all native speakers of the target language and of the appropriate age-group for the CRS-PRO questionnaire. The prevalence of CRSwNP increased with age in adults (≥ 18 years of age), particularly after 40 years of age eventhough CRSsNP was more prevalent in subjects younger than 40 years [9]. The appropriate age-group was determined as a mean over 40 years of age to include all CRS. Patients were asked to complete the questionnaire in the presence of a practitioner who noted their reactions regarding the understandability of each item. The number of subjects interviewed, their age, the time it took to complete the questionnaire, the difficulties encountered, the solutions suggested and retained and how the third version of the questionnaire was produced were collected. Thanks to these remarks, we modified the questionnaire and obtained French version 4. This version was proof-read leading to French version 5.

Before initiating the study, all researchers were trained in patient interviewing. Oral consent was obtained from all participants. As all questionnaires were completed, there were no concerns regarding missing data.

We used questionnaires completed by patients and stored results in a secure database. To test the reproducibility of this new scale, test‐retest reliability was assessed in 10 patients. Patients answered the questionnaire again under the same conditions 7 days later. Consistency between responses was evaluated using intra-class correlation coefficient. The closer the coefficient to 1, the higher the repeatability. The statistical analyses were performed using R software (v. 1.3.10703, R Foundation for Statistical Computing, Vienna, Austria, www.r-project.org). P-values were calculated using two-sided tests.