Cofactor may refer to any of the following:

• Cofactor (linear algebra), the signed minor of a matrix
• Minor (linear algebra), an alternative name for the determinant of a smaller matrix than that which it describes
• Cofactor (biochemistry), a substance that needs to be present in addition to an enzyme for a certain reaction to take place.
• Shannon expansion (Shannon cofactor), a derived function of another function, a notion useful in computer science and mathematics.
• Cofactor (epidemiology) in epidemiology is a condition that exacerbates the effects of another condition; for instance, while chlamydia infection on its own will not cause cervical cancer, it increases the risk that HPV infection will do so.

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