Differential item functioning of the English and Chinese versions of the Fagerstrom Test for Nicotine Dependence.

Different language versions of the Fagerstrom Test for Nicotine Dependence (FTND) have been developed, but no studies have evaluated measurement equivalence between the respective non-English and English versions. We investigated differential item functioning (DIF) of the English and Chinese versions using a multidimensional item response theory approach. A community sample of 409 American smokers completed the English version (n=241) and the Chinese version (n=168). Results indicated two correlated dimensions (morning and daytime nicotine dependence) of the FTND and one item (difficult to refrain) showing significant large DIF, suggesting respondents using the Chinese version were more likely to endorse this item and report more difficulty to refrain from smoking at various public places even after controlling for the nicotine dependence level. However, the impact of this DIF item was found negligible on the scale level, suggesting the acceptability of conducting scale-level analysis using both language versions. Further analysis revealed that the reliabilities of two dimensions did not meet the commonly accepted standard. Suggestions were made to improve scale reliabilities of the FTND.