Effectiveness vs Efficacy

Discussion in 'English Only' started by shiningstar, Aug 30, 2010.

  1. shiningstar

    shiningstar Senior Member


    In a paper there was a line saying that:

    It made me think what difference migth be there between these two words that I thought they are synonyms of each other.

    Why did the author make this distinction between two synonymous words? What is the difference, if any, between these two words?

    Thank you...

    Edit: There was a discussion about this subject in the forum but the content of that post is different...
  2. owlman5

    owlman5 Senior Member

    These two words are considered synonyms in many contexts. I think that we should focus on the medical meaning of "efficacy" here. Well, I just poked around in my dictionary and came up with one idea. Here's the first definition for "efficacy" in M-W: : the power to produce an effect :

    Here we have a possible explanation for the text's insistence that the two terms be used differently: If trials are merely designed to test a drug's "efficacy", then they seek only to show that the drug produces a measurable effect. I must assume here that by "interventions" the writer means "interventions with drugs".

    If trials are designed to test the effectiveness of "interventions", then they seek to prove that the interventions actually help people rather than just making them feel the effects of some drug.

    This explanation seems reasonable to me. What do you think, Shining Star?
    Last edited: Aug 30, 2010
  3. shiningstar

    shiningstar Senior Member

    If we look at it from a window that shows the difference between a pragmatic trial and an explanatory trial, then what you said here are rather reasonable. While the explanatory trials focus on the "efficacy" (i.e whether the intervention has an effect on the condition) of the intervention, pragmatic trials focus on the "effectiveness" (i.e only on the positive effect, whether it helps or not) of the interventions.

    I think I got it. Thank you owlman5:)
  4. JulianStuart

    JulianStuart Senior Member

    Sonoma County CA
    English (UK then US)
    Here is (the first page of a pdf) a paper that has an explanation of the terms as used in clinical trials. Pragmatic seeks to demonstrate the effectiveness (even being able to distinguish small differences between different treatment regimens/protocols etc.). These usually need large numbers and necessarily involve a lot of variables in terms of patient characteristics and treatment protocols. An explanatory trial seeks to minimize as many variables as possible so that a hypothesis (of cause and effect or assessing some specific relationship or theory) can be most efficiently tested - it may or may not provide the maximum benefit to the patient, but informs the clinician on how the intervention works (or not). Some early trials of new drugs or procedures (interventions) will follow this route to show that the intervention works as expected (and is safe). This is usually followed by a pragmatic trial to show how much benefit is obtained (within acceptable safety limits) in a larger "target" population, usually one with a broader range of patient variables/characteristics etc., with what is designed to be the optimized dosage scheme or intervention design.
  5. e2efour Senior Member

    England (aged 75)
    UK English
    Here are two definitions taken from http://www.emcdda.europa.eu/publications/glossary#efficacy, which may be of help.

    Effectiveness refers to whether the interventions are effective in “real-world” conditions or “natural” settings, (Flay B.R. et al.,2005). The term effectiveness is also used to describe whether a programme achieves its stated goals and produces measurable outcomes.

    Efficacy is the extent to which an intervention (technology, treatment, procedure, service, or programme) produces a beneficial result under ideal conditions....... Efficacy is distinguished from effectiveness.
  6. owlman5

    owlman5 Senior Member

    I can't speak for Shining Star, E2E Four, but I'm glad you took the time to post this information. It was news for me and very helpful.
  7. shiningstar

    shiningstar Senior Member

    Thank you all for your efforts to help and to provide correct information. I must say that the definitions (or understanding) of both terms from different sources show a contradiction going on in the science world regarding these two terms.

    What do you think?

    Edit: I just went back to the paper and read the section where the design of the trial is described. Here is the passage in which it repeats the line I wrote at my first message:

    According to this, it's my understanding of it, effectiveness refers to the benefits of the interventions. Doesn't it?
    Last edited: Aug 31, 2010
  8. pulaunias Member

    As e2efour pointed out:

    "efficacy" suggests a quantiative information, whereas "effectiveness" generally does not.

    We can say the efficacy of this drug A is better than that of drug B.

    It is not commen (as I feel) to say the effectivenss of this drug is higher that that drug. We'd better say this drug is more effective than the other.
  9. JulianStuart

    JulianStuart Senior Member

    Sonoma County CA
    English (UK then US)
    Outside fields where one m,ust distinguish certain words' meanings and shadings of meanings, I think you were right to start with, shiningstar! They are essentially synonymous. The descriptors put forth above of pragmatic studies measure effectiveness and explanatory studies assess efficacy, as a means of distinguishing the two are at best arbitrary. I was less familiar with the terms of explanatory and pragmatic and was less careful in my use of the two words you had asked about because the distinctions presented above were new to me - if I confused you, my apologies. I can say that in 25 years in the biotech drug industry we always talked about two basic kinds on clinical trials : safety and efficacy. Some early stages were , in addition to the safety studies (required for obvious pragmatic/practical reasons), were exploratory (in the terms above these would be called "explanatory" - they informed us whether the drug had the desired response in the system under study).
  10. shiningstar

    shiningstar Senior Member


    There is no need to apologise, the line I provided was confusing to begin with and I agree with you wholeheartedly. They indeed are arbitrary. I can't think of anything that is effective yet has a little efficacy, of course this depends on the desired effect as you suggested. If something has or induce the desired effect that means it's efficient, in other words it has efficacy. I mean when you measure the effectiveness of something, you ultimately measure its efficacy, even though the efficacy depends on the desired effect whether it's positive or negative.

    I think I will continue to see them as synonymous words until I'm able to distinguish them from scientific point of view.

    Again, thank you all for your priceless contribution, I really appreciate it.
  11. Marge S New Member

    In these sentences:

    clear effectiveness of ICS treatment in patient with occupational asthma still at work has not been demonstrated

    clear efficacy of ICS treatment in patient with occupational asthma still at work has not been demonstrated

    the idea is that efficacy of ICS treatment in asthma is known and demonstrated, but it may not work in patients with occupational asthma still at work; so, i'd rather use effectiveness, meaning that its usefulness in this particular conditions (and not its efficacy in general) is debated.

    What do you think? Thank you for your help

Share This Page