Health Services Research (HSR) is a relatively recent discipline which describes how health care delivery occurs and the evaluation of that care. The implementation of a Medical Emergency Team (MET) is an example of a health service intervention. The aim of the MET is to extend the expertise of Intensive Care across the hospital to all at-risk patients. The MET criteria for calling are based on simple abnormalities in vital signs with an extra "worried" category to empower junior medical and nursing staff to call for help. The concept is based on early intervention and resuscitation of the seriously ill, hopefully leading to improved outcomes from intensive care and perhaps even avoiding admission to an intensive care unit. The problems of implementing major health service change and evaluating the effectiveness of that change presents a different challenge to evaluating a new drug or procedure and is approached within different research frameworks.