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efficacy, efficiency and effectiveness

efficacy, efficiency and effectiveness

efficacy, efficiency and effectiveness

(OP)

I would be glad (and thankful) to learn about the correct use of these words in an engineering context.

RE: efficacy, efficiency and effectiveness

Efficacy and effectiveness are synanoms.

From Dictionary.com:

efficacy

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

ef?fec?tive?
–adjective
1.    adequate to accomplish a purpose; producing the intended or expected result: effective teaching methods; effective steps toward peace.

—Related forms
ef?fec?tive?ly, adverb
ef?fec?tive?ness, ef?fec?tiv?i?ty, noun

Efficiency is the ratio if two things, typically the input to a process and its ouput, in equivalent units.

RE: efficacy, efficiency and effectiveness

I believe that efficacy and effectiveness both mean success or capability of producing the intended effect. For example, "the salt spray test proved the efficacy/effectiveness of the coating that was applied to the sample to prevent corrosion."

Efficiency could be used in the same way, but in an engineering context it is most often used to mean thermodynamic efficiency that is efficiency = output power/input power. It might also be used to express effect compared to resources applied. For example, "the inexpensive coating has been proved to be an efficient means of preventing corrosion."

RE: efficacy, efficiency and effectiveness

Efficiency implies effectiveness, but not vice versa.  Many things in life are effective but inefficient.

RE: efficacy, efficiency and effectiveness

Efficiency relates to getting the most out relative to the amount you put in (most work, power, value for money, etc).

Efficacy and effectiveness both relates to how well the desired output was achieved.

If something does everything you would want it to, it is the most effective.
If another product does 90% of what you want for 10% of the cost, it is more efficient.

If 90% efficacy is acceptable go for the highest efficiency. If not you need to look at the effectiveness of the products.

RE: efficacy, efficiency and effectiveness

All three words come from the same Latin verb - 'efficere' - to achieve. We have gradually given different shades of meaning to the derivatives. 'Effectual' is another.

The engineering definition of 'efficiency' is correctly described above. However, in common usage, 'efficient' ususally means 'effective'. I'm often told how 'efficient' my log fire is, because it heats the room up nicely. Probably about 5% efficient actually!

In a technical sense, 'effective' is also used for an RMS value of an alternating or cyclical quantity.

And of course the adjective from 'efficacy' is 'efficacious'. I think that's a splendid word with a good old-fashioned ring to it. Much more imposing than 'effective'.

And as for 'efficacy' versus 'efficaciousness' - both are acceptable but the latter makes me smile more.

RE: efficacy, efficiency and effectiveness

(OP)

Thanks to all correspondents. I've noted that all these words with different nuances are meant to show the capability of producing a result. It seems to me harrisj's answer is very much to the point.

I've also seen "effectiveness" expressed as a ratio. For instance, in Computer Engineering the effectiveness level of data-processing equipment equals the ratio of the operational use time to the total performance period, expressed as a percentage. Another example: in Geology, the property of earth containing interconnecting interstices, expressed as a percent of bulk volume occupied by the interstices is called effective porosity.

On the other hand efficiency is not always a ratio with a value ≤1.0; for instance, when expressing the degree of heat output per unit of fuel when all available oxidizable materials in the fuel have been burned.

When speaking of efficacy I recall reading Perry VII in a Spanish version referring to compressors' adiabatic efficiency as adiabatic efficacy.

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