Introducción sección especial

The International Objective Measurement Workshop (IOMW) is the biennial conference from which the four articles in this special issue of PEL were drawn.  They were based on presentations given in Washington, DC, in April 2016.  The IOMW has long nurtured an interest in the philosophy and possibilities of what is called “objective measurement”, or “invariance”, specifically as implemented by the Rasch model.  That interest is as keen today as it was in the 1980’s when the conference began.  As an informal introduction, it may be useful to review what “objectivity” means, how it is rooted in the physical sciences, and why the authors of these papers consider it an important thing to have. What does it mean to do a quantitative analysis of a dataset?