Although in last decades the interpretative character of social sciences has been emphasized, that doesn?t mean there is an absence -and sometimes not even a lack of consolidation- of quantitative character researches. Is in this sense that we consider of great importance to get the discussion around the measuring issue back, but this time with a constructivist approach that does not consider the qualitative research as a permanent opposite of the quantitative one, and vice versa, having as a starting point that the main issue is not datum itself, but its construction. In this sense, we attempt to approach to the datum role and construction, in their modality of analytical constructions that are as abstracts as the qualitative ones. Summarizing, the issue is if the person, in singular and plural, is a part of the so called knowledge. As we are assuming an affirmative answer, it is necessary to argument and present the reasons that have led us to this conclusion, and to restart the discussion about its implications in the methodological, technical and discursive construction levels of social sciences. It is intended to situate the discussion on datum construction in an epistemological level, giving particular emphasis to the problem of construction-correspondence, facing those perspectives which have reduced it to its clearly technical level, which sees the problem as a mere correspondence between preciseness and accuracy. Likewise, it is intended to underline the necessity of keeping a constant epistemological vigilance during every research process. As a complement to this remarks, we present an example taking some studies about poverty and marginality in Mexico and Latin America as a basis, where the different ways in which indicators are constructed, and the variety of outputs that result from them are analyzed; this exercise allows to clearly identify the primacy of theory over observation, and at the same time it allows to find one of the reasons for divergence between the researches, and between these and the management programs .