The Accreditation Council for Graduate Medical Education Outcome Project has shifted the focus of residents' education to competency-based outcomes of learning. The challenge of meaningful assessment of learner competence has stimulated interest in the Dreyfus and Dreyfus Model, a framework for assessing skill acquisition that describes developmental stages beginning with novice and progressing through advanced beginner, competent, proficient, expert, and master. Many educators have adopted this model, but no consensus about its adaptation to clinical medicine has been documented. In this article, the authors seek to integrate generally accepted knowledge and beliefs about how one learns to practice clinical medicine into a coherent developmental framework using the Dreyfus and Dreyfus model of skill acquisition. Using the general domain of patient care, the characteristics and skills of learners at each stage of development are translated into typical behaviors. A tangible picture of this model in real-world practice is provided through snapshots of typical learner performance at discrete moments in time along the developmental continuum. The Dreyfus and Dreyfus model is discussed in the context of other developmental models of assessment of learner competence. The limitations of the model, in particular the controversy around the behaviors of "experts," are discussed in light of other interpretations of expertise in the literature. Support for descriptive developmental models of assessment is presented in the context of a discussion of the deconstructing versus reconstructing of competencies.

Previous studies have demonstrated that lung-specific proteins are associated with surfactant lipids, particularly the highly surface active subfraction known as tubular myelin. We have isolated a surfactant-associated protein complex with molecular weight components of 36 000, 32 000, and 28 000 and reassembled it with protein-free lung surfactant lipids prepared as small unilamellar liposomes. The effects of divalent cations on the structure and surface activity of this protein-lipid mixture were investigated by following (1) the state of lipid dispersion by changes in turbidity and by electron microscopy and (2) the ability of the surfactant lipids to form a surface film from an aqueous subphase at 37 degrees C. The protein complex markedly increased the rate of Ca2+-induced surfactant-lipid aggregation. Electron microscopy demonstrated transformation of the small unilamellar liposomes (median diameter 440 A) into large aggregates. The threshold Ca2+ concentration required for rapid lipid aggregation was reduced from 13 to 0.5 mM by the protein complex. This protein-facilitated lipid aggregation did not occur if Mg2+ was the only divalent cation present. Similarly, 5 mM Ca2+ but not 5 mM Mg2+ improved the ability of the protein-lipid mixture to form a surface film at 37 degrees C. Extensive aggregation of the surfactant lipids without protein by 20 mM Ca2+ or 20 mM Mg2+ did not promote rapid surface film formation. These results add to the growing evidence that specific Ca2+-protein-lipid interactions are important in determining both the structure and function of extracellular lung surfactant fractions.