Associations are a widely used construct of object-oriented languages. However, the meaning of associations for conceptual modelling of application domains remains unclear. Ontological considerations in past research suggest that associations are related to the concept of mutual properties. Specifically, previous research has suggested that mutual properties, not associations, should be modelled, and guidelines for doing this in UML have been offered. This paper presents the results of an experimental study, which suggest that this guidance does in fact lead to improved models.