When designing software architectures, an architect relies on a set of pre-defined styles commonly named architectural patterns. While architectural patterns embody high level design decisions, an architectural tactic is a design strategy that addresses a particular quality attribute. Tactics; in fact, serve as the meeting point between the quality attributes and the software architecture. To guide the architect in selecting the most appropriate architectural patterns and tactics, the interactions between quality attributes, tactics and patterns should be analyzed and quantified and the results should be considered as decision criteria within a quality-driven architectural design process. In this paper, we propose an approach for a quantitative evaluation of the support provided by a pattern for a given targeted set of quality attributes.