Considerações sobre o estudo de dimensionalidade em instrumentos de medida baseados em itens

There are many statistical techniques to verify the dimensionality of questionnaires or tests. But these dimensions need to be present in individuals and each factor (corresponding to one dimension) must be strongly associated with some subset of items. We will show in this work, by simulated datasets, if there are not items typically in one dimension, then the statistical techniques may not detect this dimension. In particular, if all the items are multidimensional, statistical techniques may suggest that the instrument is unidimensional. As a practical application are used the responses of the first part of admission process in a university (UNESP), consisting of items of different disciplines of high school. We found a dominant dimension, which allows to apply a one-dimensional model of IRT for measuring of the general proficiency. However, we verify that three-dimensional MIRT model is more appropriate, describing what is the test measuring.