Cool MateEffectiveness vs Efficacy vs Success
When to use each in English, with meaning, register, and examples.
Effectiveness
Efficacy
Success
| Effectiveness | Efficacy | Success | |
|---|---|---|---|
| Pronunciation | 🇬🇧 /["/ɪˈfektɪvnəs/","/ɪˌfekˈtɪvəti/"]/🇺🇸 /["/ɪˈfektɪvnəs/","/ɪˌfekˈtɪvəti/"]/ | 🇬🇧 //ˈɛfɪkəsi//🇺🇸 //ˈɛfɪkəsi// | 🇬🇧 /["/səkˈses/"]/🇺🇸 /["/səkˈses/"]/ |
| Meaning | How well something works or succeeds. | Effectiveness or how well something works. | When you achieve something you wanted to do. |
| Example | to check the effectiveness of the security system | The efficacy of the new vaccine was confirmed in clinical trials. | His success in the competition made him very proud. |
| Register | Neutral | Formal | Neutral |
| How common | Top 2,000 (common) | Beyond 10,000 (less common) | Top 1,000 (very common) |
| CEFR level | C1 | - | A1 |
| Part of speech | noun | noun | |
| Collocations | measure effectiveness, assess effectiveness, improve effectiveness, evaluate effectiveness | clinical efficacy, evaluate efficacy, prove efficacy, demonstrate efficacy, measure efficacy | enormous, great, immense, amount, degree, level, achieve, attain, enjoy, come, lie (in something), depend on something, rate, story, factor, with success, without success, success in, a chance of success, a hope of success, confident of success, resounding, roaring, rousing, be, prove, have, wish somebody (every) success |
| Antonyms | ineffectiveness, failure | - | failure, defeat, setback |
| Common mistakes | Confused with 'effect' — remember 'effect' is a noun meaning the result., Using 'effectiveness' when discussing personal feelings — it's more about objective results., Mispronouncing the word, often stressing the wrong syllable. | Confused with 'efficiency', which refers to doing things quickly and without waste., Often used without proper context; needs to specify what is being evaluated., Mispronounced, especially by non-native speakers. | Confused with 'successfully', which is an adverb., Used incorrectly as a verb instead of the noun form., Misplaced in sentences, such as 'We have success' instead of 'We are successful'. |
| Usage notes | Used in both formal and informal contexts, often in discussions of strategies, programs, or methods. Avoid using in overly casual conversations. | Used primarily in formal contexts like research, medicine, and discussions about policy. Less common in everyday conversation. | Use 'success' when talking about achieving goals or winning in a friendly context. Avoid using it in negative situations or as a mockery. |
Frequently asked questions: Effectiveness vs Efficacy vs Success
What's the difference between Effectiveness, Efficacy, and Success?
Effectiveness: How well something works or succeeds. Efficacy: Effectiveness or how well something works. Success: When you achieve something you wanted to do.
Which is more formal: Effectiveness, Efficacy, and Success?
Efficacy is the most formal of these.
Which is more common: Effectiveness, Efficacy, and Success?
Success is the most common in everyday English.
Which is more advanced: Effectiveness, Efficacy, and Success?
Effectiveness is the highest level, at C1, on the CEFR scale.
Can you show an example of each?
Effectiveness: to check the effectiveness of the security system Efficacy: The efficacy of the new vaccine was confirmed in clinical trials. Success: His success in the competition made him very proud.
Can I use Effectiveness, Efficacy, and Success interchangeably?
Not always. Effectiveness, Efficacy, and Success are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.