# what is time reversal test & factor reversal test? give example

Time reversal test = A test which is used to determine whether a given method will work in both ways, (i.e backward or forward) . This test provides that the formula of index number should be such that , the current on the base and the base on the current should multiply into unity(1). Such that P

_{01 }x P

_{10 }= 1 (where , 0 denotes base year and 1 denotes current year)

For ex. Fisher's Index Formula satisfies this test.

Factor Reversal test = this test holds when the price index id multiply with quantity index is equal to

= V

_{01}

Such that : P

_{01 }x Q

_{01 }= V

_{01}

For Ex. = Fisher's Index formula

Regards.

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