Most usually, linguistic validation refers to a process whereby translated text is actively tested with patients in the target population and target language group through cognitive debriefing interviews. For example, if the PRO instrument is intended to measure the symptoms of diabetes in a trial in Denmark, the linguistic validation interviews would be conducted with diabetic patients in Denmark, who speak Danish as their mother tongue. This interview exercise ensures that items are appropriate for use in the target population, are clearly expressed and understood. The exercise is also an important tool for demonstrating content validity when compared with the source. During the interview, the respondents complete the questionnaire, and then answer a series of open-ended questions on its content and explain what they think each item means in their own words. The results of this cognitive debriefing exercise should therefore show the respondents' understanding of the translation, and alterations can be made after this stage if nuances of meaning in the source text have not been clearly expressed in the translation and understood by the respondents. The process also ensures multi-lingual harmonization of the translations, by making sure that the questionnaire is understood in the same way by target populations across all language groups, thus ensuring that the resulting quantitative data can be compared across language groups.