The failure to provide a health care service when it would have produced a favorable outcome for a patient. Standard examples include failure to provide appropriate preventive services to eligible patients (e.g., Pap smears, flu shots for elderly patients, screening for hypertension) and proven medications for chronic illnesses (steroid inhalers for asthmatics; aspirin, beta-blockers and lipid-lowering agents for patients who have suffered a recent myocardial infarction).