ACFC/44DOC(2012)001 rev linguistic or cultural rights must not be made dependent on a person's proficiency in his or her minority language, nor on the person’s skills in other languages.15 17. Affiliation with a minority group is a matter of personal choice, which must, however, be based on some objective criteria relevant to the person’s identity.16 No disadvantage shall result from the choice to affiliate with a given group. Due attention must be paid to freedom of choice, especially when the declaration of affiliation with a minority is not anonymous, when it remains unchangeable for a long period, and when the refusal to declare, for instance, one’s linguistic affiliation to one of the pre-established language categories leads to exclusion from certain political or civil rights.17 The association of persons with a specific group based on visible or linguistic characteristics or on presumption without their consent is not compatible with the Framework Convention.18 18. Moreover, a person might wish to identify herself or himself with several groups. The phenomenon of multiple affiliation is in fact quite common, due to mixed marriages, for instance, or cases of state succession. A person may also identify himself or herself in different ways for different purposes, depending on the relevance of identification for him or for her in a particular situation. The Advisory Committee considers that the principle of selfidentification, as contained in Article 3 of the Framework Convention, also guarantees the possibility of multiple affiliation. This implies that, in principle, a person may claim linguistic rights with regard to several minority languages, as long as the relevant conditions, such as demand and/or traditional residence, contained in the respective articles of the Framework Convention are fulfilled. 19 1.3. Data collection 19. The Advisory Committee emphasises the importance of collecting reliable disaggregated data to draw up, implement and evaluate effectively policies that respect and promote the linguistic needs and rights of persons belonging to different groups. The collection, storage and use of such data must fully respect existing standards on personal data protection.20 Importantly, states are encouraged to collect data from a variety of sources, in addition to the population census, such as formal and informal household or school surveys, as well as independent research. When interpreting the collected data, authorities must be aware that past experience and fear of discrimination can prompt persons to hide their linguistic affiliation and identity.21 Quantitative data must therefore not be regarded as the sole means of obtaining reliable information for the design of language policies, but must be supplemented with qualitative sociological, ethnographic and other scientific studies, especially when trends reveal a decreasing number of speakers of a particular language or when statistical data differs from estimations made by minority representatives. 20. Language as a marker for ethnic belonging was introduced in the scope of the population censuses in the 19th century. Following the assumption that every person has a dominant language, all persons indicating more than one language were nevertheless usually treated as monolingual for census purposes. However, in order for language policies to respond to current challenges, they must acknowledge individual multilingualism as well as the social and linguistic diversity of contemporary societies. Speakers of minority languages 15 Second Opinion on Sweden; Second Opinion on Ukraine. Framework Convention for the Protection of National Minorities and Explanatory Report, H(1995)010, February 1995, paragraph 35. 17 First Opinion on Italy; Third Opinion on Cyprus. 18 First Opinion on Germany; First Opinion on the Slovak Republic. 19 Second Opinion on Armenia. 20 See, for example, the Convention for the Protection of Individuals with regard to Automatic Processing of Personal Data (ETS No. 108) and the Committee of Ministers’ Recommendation Rec(97)18 concerning the protection of personal data collected and processed for statistical purposes. 21 Second Opinion on Croatia. 16 7