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a means of portraying arithmetically the enduring equality between two (or more) VARIABLES that are equal by definition. For example, £1 = 100p (or $1 = 100¢), and no matter how many pounds (or dollars) we have, they can always be converted into pennies (or cents) by multiplying by 100. Identities are generally given a three-bar ‘identity’ sign (=) to indicate that the value to the left of the three bars is identical to the value to the right of the sign. The QUANTITY THEORY OF MONEY is one of the best-known examples of an identity in economics, written as:

where M is the money stock, V is the velocity of circulation of money, P is the general price level and T is the number of transactions undertaken. See EQUATION.

Collins Dictionary of Economics, 4th ed. © C. Pass, B. Lowes, L. Davies 2005
References in periodicals archive ?
Now the English word "same" is ambiguous between numerical identity (as in "This is the same ball that Sandy Koufax threw the last strike with") and qualitative identity (as in "Your car and mine are just the same").
Charmers quite explicitly claims his invulnerability to the Block version because he doesn't pin qualitative identity on the identity of the distal stimuli, so we can't now bring them in to distinguish reddish from greenish.
Either the 'and' points up a distinction, or, functioning as a true conjunction, proclaims qualitative identity. All too often in a world of non-make-believe the latter interpretation has proved scandalously true.

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