Affect versus Effect

January 3, 2017

Dr. Kathryn Sobek, Filipodia Editor


I will often see the words affect and effect used incorrectly in both medical and non-medical writing. While it is a common mistake, it is easily fixed by learning the definition of both words and a few quick tricks to remember the difference.


Affect is most commonly used as a verb and means to produce an effect upon.[1]


Effect is most commonly used as a noun and means something that is produced by an agent or cause.[2]


When I am having trouble knowing which word to use, I remember that a verb describes an action. Action starts with ‘a’ and so does affect. You could also try to substitute other verbs in place of affect/effect to see if the sentence will make sense. If it does, then affect is the correct choice. If it doesn’t, then effect is the correct choice.


RAVEN is a popular acronym that is also used to remember the difference. It stands for Remember Affect Verb Effect Noun.


Now for some examples of each:


The treatment affected the patient outcome.

The effect of the treatment on the patient outcome is unknown.


We hypothesize that the drug will affect the function of the protein.

We hypothesize that the effect of the drug will decrease the function of the protein.

  1. “affect.” 2016. (22 December 2016).
  2. “effect.” 2016. (22 December 2016).