Quantitative questionnaires are increasingly applied across different languages and cultures.
They play an important role in research on immigrant communities as well as in
surveys of the general population of which immigrants are a significant part. Because
immigrants have often limited proficiency of the language of the host country, usually
questionnaires in their first language ("mother tongue") are needed. For this purpose, it
is common to use questionnaires developed or adapted for the population of the respective
countries which immigrants originate from. The applicability of these questionnaires,
however, may be limited because of differences between both populations in terms of
language usage, amongst others resulting from language attrition. This, for example, can
be illustrated by means of the Revised Illness Perception Questionnaire (IPQ-R) applied to
Turks in Turkey and Turkish immigrants residing in Germany. Questionnaires, therefore,
must be thoroughly tested and often re-adapted to the language style and level of language
proficiency of immigrants to avoid different forms of bias. An analytical framework of
questionnaire equivalence can guide the process of testing and re-adaptation