Efficacy or Efficiency: Do You Know the Difference?

The words efficacy and efficiency are so similar in how they are spelled, pronounced, and used that they can be confused for each other. There is a difference, though. If you’ve ever wondered how to distinguish efficacy from efficiency, we’ll leave you with a greater understanding in today’s post.

The Meaning of the Word Efficacy

Efficacy refers to how well someone or something produces desired results under certain conditions. It is typically used in medical or academic contexts.

Here is an example of efficacy being used correctly in a sentence:

Scientists are preparing a white paper about the efficacy of the vaccine in combating the illness.

As you can see, the word suggests an assessment of ability to affect an outcome.

You may also often see this word in the phrase self-efficacy, which applies to an individual’s belief about whether or not they can accomplish particular goals.

Outside of medical and certain academic fields, neither efficacy nor self-efficacy is common in daily communication, unlike our next word.

The Meaning of the Word Efficiency

Efficiency is related to efficacy, but it has a different focus. Instead of measuring whether something can produce a certain result, it applies to creating an outcome with a productive use of resources.

This subtle variation is important for meaning and context. For instance, the efficacy of modern gasoline engines has long satisfied our need for transport; however, their efficiency is still always improving in their ability to use fewer resources (fuel) to achieve the same result.

Most people will probably include the word efficiency in their writing and speech far more often than they do efficacy, particularly in business and professional writing.

Pop Quiz

Choose the correct word in each sentence below.

1. Tom got the job done, but I can’t say much for his [efficacy / efficiency] or work habits.

2. Janet’s study on the [efficacy / efficiency] of synthetic vaccines is expected to be published soon.

3. [Efficacy / Efficiency] was never a priority in that department, so we wasted lots of time and money.

4. It takes a strong sense of self-[efficacy / efficiency] to become fluent in a second language as an adult.

5. With tougher fuel-[efficacy / efficiency] standards, carbon footprints could be greatly reduced.

 

Pop Quiz Answers

1. Tom got the job done, but I can’t say much for his efficiency or work habits.

2. Janet’s study on the efficacy of synthetic vaccines is expected to be published soon.

3. Efficiency was never a priority in that department, so we wasted lots of time and money.

4. It takes a strong sense of self-efficacy to become fluent in a second language as an adult.

5. With tougher fuel-efficiency standards, carbon footprints could be greatly reduced.

 

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