Work constraints leads to accident: Questionnaire validity and a qualitative interpretation of the cutoff point

French-speaking ergonomists conceive constraint as a work situation in which the worker has his power to act, think and decide reduced or hampered, which can facilitate the occurrence of work accidents. A questionnaire with five items was elaborated to measure constraint addressed to nursing staff members. From February to September 2013, a census was carried out at Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, Brazil, one of the biggest hospital complexes in the world. The census response rate was approximately 92%. The construct validity and criterion's of the questionnaire was checked. After the former, four items remained, two of these measured time constraint and the other two Personal Protection Equipment constraint. The gold standards of the criterion validity were work accident involving exposure to biological fluid (WABIF) caused by sharp objects, WABIF through patient's body fluid contact and work incident (or almost accident) involving these two kinds of WABIF. Criterion validity was performed with both Item Response Theory (IRT) and Classical Test Theory (CTT) paradigms using logistic regression. Only WABIF by contact and incident got criterion validity. The results of the IRT paradigm showed that it is possible to go beyond the CTT cutoff point and reach a more qualitative interpretation when a relationship is established between the cutoff point value and the b parameter value of the category of each item. Hence, we find the intensity of the item (represented by its category) sufficient to him/her being at that risk.