crosscultural validation of the turkish fourdimensional symptom questionnaire 4dsq using differential item and test functioning dif and dtf analysis background the fourdimensional symptom questionnaire 4dsq is originally a dutch 50 item questionnaire developed in primary care to assess distress depression anxiety and somatization we aimed to develop and validate a turkish translation of the 4dsqmethods the questionnaire was translated using forward and backward translation and pilot testing turkish 4dsqdata were collected in 352 consecutive adult primary care patients for comparison gender and age matched dutch reference data were drawn from a larger existing dataset we used differential item and test functioning dif and dtf analysis to validate the turkish translation to the original dutch questionnaire through additional inquiry we tried to obtain more insight in the background of dif in some itemsresults twentyone items displayed dif but this impacted only the distress and depression scores inquiry among turkish people revealed that the reason for dtf in the distress scale was probably related to unfavourable socioeconomic circumstances on the other hand the likely explanation for dtf in the depression scale appeared to be grounded in culturally and religiously determined optimistic beliefs raising the distress cutoffs by 2 points and lowering the depression cutoffs by 1 point ensures that individual turkish 4dsq scores be correctly interpretedconclusions the turkish translation of the 4dsq named drtboyutlu yaknma listesi 4byl measures the same constructs as the original dutch questionnaire turkish anxiety and somatization scores can be interpreted in the same way as dutch scores however when interpreting turkish distress and depression scores dtf should be taken into account