“Efficacy describes the technical relationship between the technology and its effects (whether it actually works), whereas effectiveness concerns the extent to which application of an efficacious technology brings about desired effects (changes in diagnoses, altered management plans, improvement in health)…Efficiency is an economic concept which relates efficacy and effectivness to resource use. Assessment of efficiency is concerned with whether acceptable efficacy and effectiveness are achieved with the most prudent or optimal mix or resources.
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[Link]
AB's Reflections 