What is Fisher's ideal index number? Why is it called ideal?

Question

Accepted Answer

Fisher's index number is the geometric mean of Laspeyre's and Paasche's index numbers: $I_F = \sqrt{I_L 	imes I_P}$. It is called ideal because:
- It considers quantities of both the base year and current year
- It satisfies both time reversal and factor reversal tests
- It uses geometric mean which is the best average
- It is free from bias as it balances demerits of Laspeyre's and Paasche's