TEST FOR ITEM BIAS IN A QUALITY-OF-LIFE QUESTIONNAIRE

Item bias (differential item functioning) analysis examines whether th e construction of an index from two or more variables results in bias in relation to sex, age, or other criteria. Item bias may lead to erro neous conclusions because of distortion or dilution of the effects mea sured. In comparing groups, item bias analysis, tests whether the info rmation about possible differences between groups, obtained by the var iables constituting an index, are correctly passed on by the index sco re. We examined a quality of life questionnaire answered by 1189 breas t cancer patients. We found age-bias or bias in the comparison of grou ps receiving different treatments in three out of nine indexes. Recomm endations for the interpretation of these indexes are made. Item bias analysis is a useful method examining an issue not covered by traditio nal psychometric tests.