This article presents a strategy to improve comparisons in observational studies. We illustrate this strategy by analyzing the case of Chaitén after the volcanic eruptions of 2008. As a result of this natural disaster, that city suffered the overflow of the Blanco River, leaving the city divided between the north and south sectors. The Chilean State declared Chaitén to be uninhabitable until 2011, where it exclusively authorized the occupation of the northern sector. To date, both sectors have been occupied, marking a sharp difference between regular and irregular settlements. We use this distinction to identify the effect that living in an irregular settlement has on trust and cooperation. In order to do this, we analyzed qualitative information and survey data from 2015. In a first step, the analysis of qualitative information indicates a significant process of self-selection of the subjects in the treatment conditions. Then, we designed valid comparisons based on a Full Matching method for analyzing the effects on the dependent variables. The results indicate that, on average, living in irregular
settlements increased cooperation. However, there may be a strong heterogeneity in the way that the agents respond to the interventions here analyzed. As a consequence, in order to improve the interpretation of these results, it would be necessary to take into account other factors not observed in the data here analyzed. We finish this study by developing a series of implications for the design and planning of observational studies, in general.