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Tuesday, March 11, 2008

Efficacy - evaluated for its usefulness in controlled conditions

052. When a drug is evaluated for its usefulness in controlled conditions, it is termed as a trial signifying:

1. Efficacy

2. Effectiveness

3. Efficiency

4. Effect modification


1. Efficacy


Sabiston 15th Edition Chapter 3 - A BRIEF HISTORY OF OUTCOMES RESEARCH






Statistics Books


Efficacy can be defined as

Ä The capacity or power to produce a desired effect; "concern about the safety and efficacy of the vaccine"

Ä In general, efficacy is the ability to produce an effect, usually a specifically desired effect. For example, an efficacious vaccine has the ability to prevent or cure a specific illness. In medicine a distinction is often drawn between 'efficacy' and 'effectiveness'. Whereas efficacy may be shown in clinical trials, effectiveness is demonstrated in practice. The concept of 'self-efficacy' is an important one in the self-management of chronic diseases.

Ä (Of a drug or treatment). The maximum ability of a drug or treatment to produce a result regardless of dosage. A drug passes efficacy trials if it is effective at the dose tested and against the illness for which it is prescribed.

Ä The effectiveness or ability of a drug to control or cure an illness.


  1. Efficacy is finding how well the intervention works under IDEAL Conditions or controlled conditions
  2. Effectiveness is finding out how well the intervention works under practical conditions
  3. Efficiency is finding out how well the resources are used
  4. Effect modification describes the change due to the cause (intervention)


If you are confused between Efficacy and effectiveness, let me give an example.

Ä Drain all the petrol from you bike. Note the odometer reading. Just add 100ml. Drive at a constant speed of 40 kilometres per hour in a highway. Note the reading when the petrol has been exhausted. Now look at the kilometers covered. If you multiply this my 10, then you will know the mileage of the vehicle per litre “under test conditions”. This is what they advertise prominently and this is Efficacy

Ä Now when you put in a litre of petrol and drive from your home to hospital in the streets, you will find that the vehicle does not “give” the mileage advertised, because you use the vehicle under “practical conditions”. This is effectiveness.


Efficiency is how well you use the petrol (That is by avoiding rash driving, maintaining constant pressure in tyres, regular servicing) given to you

1 comment:

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