The requirements elicited from stakeholders suffer from various afflictions, including informality, vagueness, incompleteness, ambiguity, inconsistencies, and more. It is the task of the requirements engineering process to derive from these a formal specification that truly captures stakeholder needs. The Desiree requirements engineering framework supports a rich collection of refinement operators through which an engineer can iteratively transform stakeholder requirements into a specification. The framework includes an ontology, a formal representation for requirements, as well as a tool and a systematic process for conducting requirements engineering. This paper reports the results of a series of empirical studies intended to evaluate the effectiveness of Desiree. The studies consist of three controlled experiments, where students were invited to conduct requirements analysis using textbook techniques or our framework. The results of the experiments offer strong evidence that with sufficient training, our framework indeed helps users conduct more effective requirements analysis.