The phrase "an external factor" is correct and usable in written English.
It can be used when discussing influences or elements that originate outside a particular system or situation.
Example: "The project's success was influenced by an external factor, such as market trends."
Alternatives: "an outside influence" or "a foreign element."
That, he said, puts their happiness under the control of an external factor -- little better than luck and whim.
Often, the dramatic tension in stories of the "married man meets forbidden woman" type comes from an external factor — the wife's suspicions, the man's fears for his eternal soul.
Others point to an external factor: the presence of Tim Cahill, the state treasurer, in the race as an independent candidate.
This has led to the agency theory of motivation, where it is argued that autonomy is better than financial reward for motivating people, as a reward is an external factor, beyond their control and could be taken away at any time, whereas giving someone autonomy means they have control and responsibility so a sense of achievement, which could explain why micromanagement is so infuriating.
That is certainly an "external factor".
When MSCs are treated with an external factor, their differentiation ability may be improved.
This was further extended by adding perceived risk as an external factor.
It occurs when data sets change inherently in one direction, not because one variable depends on the other, but due to an external factor.
During the diffusion of the technology, the technology's market success, an external factor, stimulated ongoing improvements in shoe press technology.
This immanence of meaning and the totality it constituted was, however, lost in the subsequent historical development, transforming form into an external factor to life.
As an external factor restraining personal behavior, each institution's implementation and adaptation over different periods and across different communities will certainly affect individual behavior.
