New knowledge and understanding about improving the quality and reducing the costs of care will come from careful scrutiny of the variations in the outcomes of nursing interventions. Nurses need to systematically identify and measure outcomes, understanding the probabilistic nature of these patient responses to the care received. Using a formative evaluation process, nurses should measure degrees of patient outcomes over time to ascertain the effects of nursing care and analyze the variances in these observed outcomes from what was expected. Critical pathways are valuable tools for guiding evaluations of nursing care along a timeline and can lead to improvements in nursing care.