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Affect or effect?


Affect or effect?

The basics

‘Affect’ is a verb. It means to influence something, e.g.

Diet affects a person’s risk of cancer.

Diet actively influences a person’s risk of cancer.

‘Effect’ is a noun. It means an outcome, i.e., the result of an action:

An effect of global warming is poorer air quality.

We are describing the result (‘poorer air quality’) of an action (‘global warming’).

‘Affect’ and ‘effect’ are often interchangeable

X has an effect on Y.

X is affected by Y.

These statements have the same meaning.

A quick reminder of verb tenses

Remember, only ‘affect’ is a verb, whereas ‘effect’ is a noun. The following table only applies to ‘affect’. For more information, see our blog Verb tenses in scientific manuscripts.

Verb tenseWhen to useExample
PresentUse when stating general truths.Diet affects a person’s risk of cancer.
Present perfectUse when describing actions that happened in the past but are still relevant today.In this study, we focus on how the Great Recession has affected the iconic “American Dream.”
PastUse when discussing previous studies or past events.A quarter of all obese patients were affected by severe sleep apnea.
Past perfectUse when describing an action that occurred before another action.Telephone interviews were conducted with private households which had been affected by the 2013 floods in Germany.
Past continuousUse when describing an ongoing action that occurred in the past.It was found that the cutting strategy was affecting the geometry of second-order microstructures.
Present continuousUse when describing events that are happening at the moment of writing.The purpose of this study was to investigate what factors are affecting job-seeking stress in nursing students.
FutureUse when discussing the implications of the study.Flooding events will affect more people in the future as a result of sea-level rises.

Quick ways to identify a noun

Remember, ‘effect’, as a noun, will likely be preceded by definite/indefinite articles, e.g., ‘an effect’, ‘its effect’, ‘the effect’ … etc.

Alternative verbs/nouns

You may find it helpful to use an alternative verb/noun to help you decide whether to use ‘affect’ or ‘effect’. If the meaning of the statement is retained using an alternative verb, then ‘affect’ is correct. If the meaning of the statement is retained using an alternative noun, then ‘effect’ is correct.

Alternative verbs for ‘affect’Example
ChangeDiet changes a person’s risk of cancer.
AlterDiet alters a person’s risk of cancer.
InfluenceDiet influences a person’s risk of cancer.
Alternative verbs for ‘effect’Example
Resultresult of global warming is poorer air quality.
OutcomeAn outcome of global warming is poorer air quality.
Consequenceconsequence of global warming is poorer air quality.

Real-world examples from STEM articles

Sleep deprivation negatively affects various cognitive performances.

The effect of resistance exercise on glycemic control in type 1 diabetes is unclear.

In this study, we focused on events of severe water limitation that affect ecosystem structure and functioning.

The potential difference between the model alloys and aluminum was ­­­affected by pH value.

We investigated the effects of temperature on thermophilic anaerobic digestion of cattle manure.

Global warming will affect the genetic diversity and uniqueness of Lycaena helle populations.

All cultivars grown were affected at approximately 5 to 35% symptomatic plants per field.

In this study, we examine the factors affecting biomass enzymatic reactivity.

The high molecular weight glutenin subunits were the most affected.

Aspirin has shown a protective effect in population-based studies.

Naturally occurring VHL mutations have been evaluated to determine their effect on HIF-a ubiquitination.

A favorable effect of high intakes of milk and yogurt has been suggested by a hospital-based case-control study.

In addition to its effect on p53 checkpoint function, deletion of p14AR7 also affects the expression of p27.

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