Inter-Quartile Range is defined as the difference between two extreme quartiles of a series,

Thus, absolute IQR = Q_{3} – Q_{1}

And Coeff.IQR Q_{3} – Q_{1/ Q3 + Q4}

Where, Q3 = Upper quartile of a series

and Q1 = Lower quartile of a series.

From the formula cited above, it must be clear that the determination of the IQR depends entirely upon the values of the two extreme quartiles i.e., Q3 and Q1.

**Merits and Demerits**

The relative merits, and demerits of IQR can be pointed out as under:

**Merits**

- It is rigidly defined.
- It is simple to calculate.

**Demerits**

- It is not based on all the observation of the series, since first 25%, and last 25% of the series are completely ignored in its calculation.
- It is not capable of further algebraic treatment.
- It does not give any idea of dispersion of the items from the central value of the series.
- It is affected by fluctuations in sampling.

It takes more time to calculate as it involves determination of the two quartiles in the first instance.