Formulas
According to Laakso and Taagepera (1979) the effective number of parties is computed by following formula:
Where n is the number of parties with at least one vote/seat and the square of each party’s proportion of all votes or seats. This is also the formula for the inverse Simpson index, or the true diversity of order 2.
An alternative formula proposed by Golosov (2010) is
which is equivalent - if we only consider parties with at least one vote/seat - to
Here, n is the number of parties, the square of each party’s proportion of all votes or seats, and is the square of the largest party’s proportion of all votes or seats.
Read more about this topic: Effective Number Of Parties
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“You treat world history as a mathematician does mathematics, in which nothing but laws and formulas exist, no reality, no good and evil, no time, no yesterday, no tomorrow, nothing but an eternal, shallow, mathematical present.”
—Hermann Hesse (1877–1962)
“That’s the great danger of sectarian opinions, they always accept the formulas of past events as useful for the measurement of future events and they never are, if you have high standards of accuracy.”
—John Dos Passos (1896–1970)
“It is sentimentalism to assume that the teaching of life can always be fitted to the child’s interests, just as it is empty formalism to force the child to parrot the formulas of adult society. Interests can be created and stimulated.”
—Jerome S. Bruner (20th century)