Effectiveness

Effectiveness is the extent to which a particular health technology (medical device, drug, procedure, health program, or health service, including interventions) does what it is intended to do (i.e., leads to a beneficial health outcome or result) when it is provided under clinical practice conditions or in the field.

The basic conceptual difference between effectiveness and efficacy of a given medical technology lies in the conditions under which it is provided and estimated. Efficacy refers to its benefits when it is deployed under ideal conditions (under the highest possible control of variables) and effectiveness when it is provided under realistic conditions, such as those encountered in clinical practice.

The effectiveness of a particular health technology can be established or estimated by means of different quasi-experimental and observational study designs. The selection of a study type to estimate the effectiveness of a given health technology depends, among other factors, on the objectives of the study, the conditions under which it has to be carried out, and the availability and the type of data that must be observed.

It is important to clearly distinguish among effectiveness, efficacy, and efficiency (the relationship between the cost or the resources used to provide a specific treatment, intervention, program, or procedure and the results obtained), since they are often confused.

In practice, efficacy and effectiveness of the same medical technology differ, and the former should not be necessarily considered an accurate estimate of the latter. For example, the efficacy of a vaccine or a drug, estimated in a randomized controlled trial, tends to be higher than its effectiveness. The degree of control of variables that is usually attained during the administration of a vaccine or a drug in a randomized trial can almost never be reached during their administration in clinics, primary health care centers, or hospitals. Reasons why the health benefits expressed by efficacy are greater than those referred by effectiveness often include the following

• The cold chain can fail (i.e., the drug may not be stored at the proper temperature).
• Doses of the active principle of the drug contained in the tablets may vary.
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• The clinical characteristics of patients may differ from those of the individuals who participated in the randomized trial, or the spectrum of the disease covered can be different.
• Patient compliance to the prescribed treatment regime is difficult to control, and the degree of adherence often changes according to different factors related to the patient's psychological profile or educational level, the mechanisms for providing health care, accessibility of health services, or, in general, the way in which health services are delivered.

Examples of endpoints (primary or secondary events observed in a patient during the course of a treatment or in a health program during its implementation) usually used to estimate effectiveness are as follows: the 1-year survival rate of patients with a particular type of neoplasm treated with chemotherapy in an outpatient service at a university hospital, the percentage of hypertensive patients with systolic and diastolic pressure adequately controlled after 1 year of treatment in a primary health care center, the 5-year death rate of women enrolled in a breast cancer early detection program, and the postoperative infection rate in surgical patients enrolled in an antibiotic prophylaxis for surgical infections program.

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